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  • American Institute of Physics (AIP)  (49,883)
  • 1995 - 1999  (49,883)
  • 1
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Laser Evaporation Ion Source (LEVIS) active lithium ion source has been developed for use on the focusing ion diode operated on the 10 TW Particle Beam Fusion Accelerator-II (PBFA-II) [J. P. VanDevender and D. L. Cook, Science 232, 831 (1986)] at Sandia National Laboratories. The source configuration consists of two laser pulses impinging on a heated (200 °C) thin-film LiAg layer on the anode surface. A short-pulse Nd:YAG laser creates a high-density vapor, which is then ionized by a long-pulse dye laser using the LIBORS (laser ionization based on resonant saturation) ionization method. Small-scale experiments determined that this dual laser-based approach can produce a source plasma of adequate density and confinement for acceleration and transport. Hardware modifications were undertaken to correct problems of premature impedance collapse and lack of beam lithium seen on previous PBFA-II experiments. As much as 85 kJ of Li is measured at the beam focus, but the source may not have been operating in a fully active (i.e., preformed) manner. Focusing performance appears superior to a passive LiF ion source operated on PBFA-II with the same magnetic field topology. © 1999 American Institute of Physics.
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  • 2
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    Physics of Plasmas 6 (1999), S. 3717-3720 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Two fluid equilibrium solutions for intense ion beam transport in low-pressure gas or vacuum are derived. The equilibria that are most relevant to beam transport have neutralizing electrons drifting in the same direction as the beam. These solutions require a small net positive charge within the beam channel to support an equilibrium radial electric field to allow the electrons to E×B drift axially. At the extremes of the domain of allowable solutions this electric field approaches zero and complete charge neutrality is achieved. In this case, two solutions are obtained. The first describes ballistic beam transport with complete neutralization of the beam current by the electrons, and the second describes pinched beam transport with no neutralizing electron current. Equilibria between these two extremes exhibit both a small net positive charge within the beam channel and partial current neutralization. © 1999 American Institute of Physics.
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  • 3
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    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 3721-3723 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
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  • 4
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this paper we apply the recently developed state-specific multireference coupled-cluster and perturbation theories to calculate electrical properties such as dipole moment and static polarizability using perturbed orbitals in finite fields. The theories are built on complete active space reference functions, and are designed to treat quasidegeneracy of varying degrees while bypassing the intruder problem. Numerical results are presented for the model systems H4 with trapezoidal geometry and the lowest two singlet states of CH2. Both the systems require a multireference formulation due to quasidegeneracy. In the field-free situation, the former encounters intruders at an intermediate trapezoidal geometry in the traditional treatment using effective Hamiltonians, while the latter shows a pronounced multireference character in the two singlet states. This affects the response properties in the presence of a perturbing field. A comparison with the full CI results in the same basis indicates the efficacy of the state-specific methods in wide ranges of geometries, even when the traditional effective Hamiltonian based methods fail due to intruders. © 1999 American Institute of Physics.
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  • 5
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this paper we present Z-vector formalism for the Fock space multireference coupled cluster framework. We present detailed equations describing the derivative effective Hamiltonian, where the response amplitudes of the highest Fock sector are eliminated. We discuss the conditions and approximations under which the formalism is possible. We also discuss the implications and comparison with the similar formalism in the single reference framework. The computational advantages and feasibility are also commented upon in this paper. © 1999 American Institute of Physics.
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  • 6
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    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 3837-3845 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Ten low-lying electronic states of Fe(II) porphine, 5A1g, 5Eg, 5B2g, 3A2g, 3B2g, 3Eg(A), 3Eg(B), 1A1g, 1B2g, and 1Eg states, are studied with multiconfigurational second-order perturbation (CASPT2) calculations with complete active space self-consistent field (CASSCF) reference functions with larger active space and basis sets. The enlargement of active space and basis sets has no influence on the conclusion of a previous multireference Møller–Plesset perturbation (MRMP) study. The present CASPT2 calculation concludes that the 5A1g state is the ground state. A relativistic correction has been performed by the relativistic scheme of eliminating small components (RESC). For energetics, no significant contribution from the relativistic correction was found. The relative energies and orbital energies are not changed appreciably by the introduction of a relativistic correction. The present result does not agree with all the spectroscopic observations, but is consistent with a magnetic moment study. © 1999 American Institute of Physics.
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  • 7
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    The Journal of Chemical Physics 111 (1999), S. 3846-3854 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The two-body interaction energies of the cyclic (C3h) and noncyclic (C2) trimers at the basis set limit (15.55 and 16.55 kJ/mol) were estimated by means of second-order Møller–Plesset perturbation theory including terms linear in the interelectronic distance (MP2-R12 approach). Coupled cluster calculations with single and double substitutions and with noniterative triple excitations [CCSD(T)] were carried out to correct the MP2-R12 two-body interaction energies for the effect of higher excitations, and also for the evaluation of the three-body interaction energies. The calculated bonding energies of the trimers using this model calculation (16.82 and 17.20 kJ/mol) suggest that the two isomers are nearly isoenergetic. The three-body terms are small (only of the order of 1 kJ/mol), stabilizing the cyclic trimer, but destabilizing the noncyclic trimer. © 1999 American Institute of Physics.
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  • 8
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    The Journal of Chemical Physics 111 (1999), S. 3855-3861 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The structure and the relative stability of the ethanol dimer and the cyclic ethanol trimer were studied using density functional theory methods. The geometries of the different dimers and trimers were optimized at the B3LYP/6-311+G(d,p) level of theory, while the final energies were obtained at the B3LYP/6-311+G(3df,2p) level. Four different (ethanol)2 complexes were found to be local minima of the potential energy surface, the global minimum being that in which both monomers exhibit a trans conformation. The hydrogen bond (HB) in ethanol dimer is slightly stronger than in methanol dimer, reflecting the enhanced intrinsic basicity of ethanol with regards to methanol. The OH donor stretch appears redshifted by 161 cm−1, while the redshifting undergone by the OH acceptor stretch is negligibly small. The relative stability of the trimers is a function of the number of monomers with a gauche conformation, the global minimum being that in which the three monomers have a trans conformation. As for water and methanol trimers, the three HBs in the cyclic ethanol trimer are not strictly equivalent. Consistently, the redshiftings of the OH stretching frequencies are different. Cooperative effects are sizably large, as reflected in the O(centered ellipsis)O distances, the elongation of the OH donor groups, the charge density at the bond critical points, the frequency shiftings of the OH stretches, and the additivity interaction energy. The most significant features of the vibrational spectra of the monomers, the dimers, and the trimers in the 800–1200 cm−1 region are reasonably well reproduced by our calculations.© 1999 American Institute of Physics.
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  • 9
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A new potential energy surface for the lowest 3A″ electronic state of the O(3P)+HCl system is presented. This surface is based on electronic energies calculated at the multireference configuration interaction level of theory with the Davidson correction (MR-CI+Q) using the Dunning cc-pVTZ one-electron basis sets. The ab initio energies thus obtained are scaled using the scaled external correlation (SEC) method of Brown and Truhlar. The SEC-scaled energies are fitted to a simple analytical expression to yield a potential energy surface which correlates the reactants O(3P)+HCl(1Σ+) to the products OH(2Π)+Cl(2P). The reaction barrier on this surface lies at an O–H–Cl angle of 131.4° at an energy of 9.78 kcal/mol above the asymptotic O+HCl minimum. This barrier is 1.3 kcal/mol higher than that on the potential energy surface obtained by Koizumi, Schatz, and Gordon (KSG) [J. Chem. Phys. 95, 6421 (1991)] and 1.1 kcal/mol lower than the S2 surface of Ramachandran, Senekowitsch, and Wyatt (RSW) [J. Mol. Struct. (Theochem) 454, 307 (1998)]. The dynamics of the reaction O(3P)+HCl(v=2; j=1,6,9)→OH(v′,j′)+Cl on this potential surface is studied using quasi-classical trajectory (QCT) propagation and the results are compared to the experimental observations of Zhang et al. [R. Zhang, W. J. van der Zande, M. J. Bronikowski, and R. N. Zare, J. Chem. Phys. 94, 2704 (1991)]. The broad distribution of collision energies in the experiment is modeled by computing weighted averages of the quantities of interest with the weighting factor at each collision energy determined by the collision energy distribution. © 1999 American Institute of Physics.
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  • 10
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: High-resolution Stark effect measurements on the S1←S0(ππ*) origin of cis-free base isobacteriochlorin in single crystals of n-octane at 5 K are reported. The spectral splittings of the band at 15 822 cm−1 are linearly dependent on the applied electric field. The change in dipole moment (Δμ) was found to be 1.32 D and is parallel to the crystal's b-axis. This band blueshifted as the polarity of the solvents at room temperature was increased, which implies that Δμ is negative. To rationalize the large magnitudes and opposite signs of the cis and trans tautomers' Δμ values, we propose a simple valence-bond model based on ionic resonance structures. © 1999 American Institute of Physics.
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  • 11
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    The Journal of Chemical Physics 111 (1999), S. 3616-3622 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present classical molecular dynamics simulations of the solvation dynamics of a strongly polar dye molecule in a weakly polar solvent. Solvation times and amplitudes are compatible with recent measurements. Several differences in the solvation dynamics relative to the widely studied case of strong polar solvents are exhibited: lesser importance of the inertial component of the Stokes shift, relaxation times close to individual solvent reorientational times, instead of the longitudinal relaxation time of the solvent, large amplitudes of translational and orientational relaxation over about 10 ps and the presence of a long-lived solvation shell in the excited state. © 1999 American Institute of Physics.
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  • 12
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    The Journal of Chemical Physics 111 (1999), S. 3654-3667 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a molecular theory for investigating the dynamics of ions in polar liquids. The theory is based on the interaction-site model for molecular liquids and on the generalized Langevin equation combined with the mode-coupling theory. The velocity autocorrelation function, diffusion and friction coefficients of ions in water at 25 °C and at infinite dilution are studied. The theoretical results for the velocity autocorrelation functions exhibit a gradual change from oscillatory to monotonic decay as the ion size increases. The diffusion (friction) coefficients of ions in aqueous solutions pass through a maximum (minimum) as a function of the ion size, with distinct curves and maxima (minima) for positive and negative ions. These trends are in complete accord with those of the molecular dynamics simulation results performed on the same system by Rasaiah and co-workers [J. Phys. Chem. B 102, 4193 (1998)]. It is worthwhile to mention that this is the first molecular theory that is capable of describing the difference in the dynamics of positive and negative ions in aqueous solutions. A further analysis of the friction coefficients of ions in water is presented in which the friction is decomposed into the "Stokes," dielectric and their cross terms. The Stokes and dielectric terms arise from the coupling of the ion dynamics to essentially the acoustic dynamics of the solvent via the short-range interaction, and from the coupling to the optical mode of the solvent via the long-range interaction. The most striking feature of our results is that the Stokes friction so defined does not increase monotonically with increasing ion size, but decreases when ions are very small, implying a formation of a molecular "complex" comprising the ion and its nearest neighbor solvent molecules. Interesting observations concerning the cross term are: (1) its magnitude is rather large for small ions and cannot be neglected at all, and (2) the cross term for small ions seems to cancel out the Stokes part, and consequently the total friction for small ions seems to be to a large extent determined by its dielectric component. © 1999 American Institute of Physics.
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  • 13
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    The Journal of Chemical Physics 111 (1999), S. 3668-3674 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We study the drift mobility of a molecular polaron in the presence of an external applied field and Coulomb traps. The model is based on one previously developed for geminate recombination of photogenerated charge carriers. It is shown that the unusual combination of Poole–Frenkel-like field dependence and non-Arrhenius temperature dependence of the mobility, measured experimentally in molecular films, is well reproduced by this model. Our key result is that this nearly universal experimental behavior of the mobility arises from competition between rates of polaron trapping and release from a very low density of Coulomb traps. © 1999 American Institute of Physics.
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  • 14
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    The Journal of Chemical Physics 111 (1999), S. 3675-3678 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: It is known that the presence of cations like Ca++ or Pb++ in the water subphase alters the pressure-area isotherms for fatty acid monolayers. The corresponding lattice constant changes have been studied using x-ray diffraction. Reflection-absorption spectroscopy has been used to probe the chemical composition of the film. We report on the first measurements of the time evolution of the shear viscosity of arachidic acid monolayers in the presence of Ca++ ions in the subphase. We find that the introduction of Ca++ ions to the water subphase results in an increase of the film's viscosity by at least three orders of magnitude. This increase occurs in three distinct stages. First, there is a rapid change in the viscosity of up to one order of magnitude. This is followed by two periods, with very different time constants, of a relatively slow increase in the viscosity over the next 10 or more hours. The corresponding time constants for this rise decrease as either the subphase pH or Ca++ concentration is increased. © 1999 American Institute of Physics.
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  • 15
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In the interaction of low energy F2 with Si(100) at 250 K, a dissociative chemisorption mechanism called atom abstraction is identified in which only one of the F atoms is adsorbed while the other F atom is scattered into the gas phase. The dynamics of atom abstraction are characterized via time-of-flight measurements of the scattered F atoms. The F atoms are translationally hyperthermal but only carry a small fraction (∼3%) of the tremendous exothermicity of the reaction. The angular distribution of F atoms is unusually broad for the product of an exothermic reaction. These results suggest an "attractive" interaction potential between F2 and the Si dangling bond with a transition state that is not constrained geometrically. These results are in disagreement with the results of theoretical investigations implying that the available potential energy surfaces are inadequate to describe the dynamics of this gas–surface interaction. In addition to single atom abstraction, two atom adsorption, a mechanism analogous to classic dissociative chemisorption in which both F atoms are adsorbed onto the surface, is also observed. The absolute probability of the three scattering channels (single atom abstraction, two atom adsorption, and unreactive scattering) for an incident F2 are determined as a function of F2 exposure. The fluorine coverage is determined by integrating the reaction probabilities over F2 exposure, and the reaction probabilities are recast as a function of fluorine coverage. Two atom adsorption is the dominant channel [P2=0.83±0.03(95%, N=9)] in the limit of zero coverage and decays monotonically to zero. Single atom abstraction is the minor channel (P1=0.13±0.03) at low coverage but increases to a maximum (P1=0.35±0.08) at about 0.5 monolayer (ML) coverage before decaying to zero. The reaction ceases at 0.94±0.11(95%, N=9) ML. Thermal desorption and helium diffraction confirm that the dangling bonds are the abstraction and adsorption sites. No Si lattice bonds are broken, in contrast to speculation by other investigators that the reaction exothermicity causes lattice disorder. © 1999 American Institute of Physics.
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  • 16
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: High translational energy adsorption of oxygen on the (111) surface of platinum was examined with electron energy loss spectroscopy (EELS) and molecular beam techniques. EEL spectra indicate that over an incident energy range of 0.2–1.37 eV and on a Pt(111) surface held at 77 K, oxygen adsorbs in an associative chemisorbed state—yielding to the dissociated state only after sufficient substrate heating. Simple direct dissociation appears negligible for all incident kinetic energies studied. At near-zero surface coverages, exclusive population of the peroxolike molecular precursor is observed for adsorption at these high translational energies, while both superoxolike and peroxolike forms are detected for low energy adsorption (0.055 eV). This peculiarity represents evidence that translational energy is effective in differentially populating reaction intermediates and provides better quantification of potential energy barriers to dissociation. We estimate the activation barrier for dissociation from the peroxolike precursor to be approximately 0.29 eV. Initial adsorption probability measurements over a wide range of surface temperatures and high incident kinetic energies corroborate a molecular chemisorption mediated mechanism. © 1999 American Institute of Physics.
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  • 17
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    The Journal of Chemical Physics 111 (1999), S. 3714-3719 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The dissociative photoionization channels of gaseous Si(CH3)Cl3 and ion desorption mechanisms of solid-state analogs following valence-level excitation have been investigated by means of photoionization mass spectroscopy, threshold photoelectron spectroscopy (TPES), and photon-stimulated ion desorption (PSID) using synchroton radiation. The adiabatic ionization threshold of the parent molecular ion was determined to be 11.18 eV, consistent with the value of 11.16 eV obtained from the TPES spectrum. An energy shift ∼0.8 eV toward lower binding energies for the orbitals of solid Si(CH3)Cl3 with respect to the gas phase values was observed. Two thresholds at 14.97 and 17.51 eV in the CH3+ photoionization efficiency spectrum are probably associated with the ionization of 2e″ and 11a1 orbitals, respectively. The H+ desorption threshold at 20.1 eV in the PSID spectrum may be attributed to the excitation of C 2s electron correlation states to the unoccupied states. The Cl+ desorption threshold at 19.9 eV is likely initiated by an Auger-stimulated desorption process.© 1999 American Institute of Physics. [S0021-9606(99)70731-2]
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  • 18
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    The Journal of Chemical Physics 111 (1999), S. 3705-3713 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In the framework of density functional theory (DFT), a patching model for the density profile of the liquid–vapor interface is developed. The patching is based on analytical expressions of the asymptote of the density profiles. Derived from the model the surface tension of planar liquid–vapor interface as well as the Tolman length can be computed from analytic expressions. Two prototype systems are considered; the Yukawa and the Lennard-Jones. As a result, the temperature dependence of the surface tension as well as the Tolman length are obtained. The results are compared with numerical DFT calculations. © 1999 American Institute of Physics.
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  • 19
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A study of the reorientational segmental dynamics in supercooled poly(vinyl acetate) is presented, yielding detailed information about geometry and time scale of the motion close to the glass transition. The geometry information is derived from systematic variation of the evolution time in 13C 2D echo NMR measurements. The dynamics can be described as a superposition of angular jumps of approximately 10° and rotational diffusional processes. Both processes are related to the macroscopic α-relaxation. On the time scale of one jump process the orientation of a segment changes by about 2° via small step diffusion (<0.6°). Furthermore the temperature dependence of this reorientatinal scenario is analyzed within the limits imposed by the experiment. All results are compared with previous 2H 2D NMR measurements on low-molecular glass formers. In both cases the loss of correlation, as described by conventional correlation times, results from a sequence of many distinct reorientational steps. © 1999 American Institute of Physics.
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  • 20
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    The Journal of Chemical Physics 111 (1999), S. 3728-3732 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We study thin, symmetric AB-copolymer films between neutral walls using the bond fluctuation model. Near the surface, the monomer distribution with respect to the chains' center of mass is nonisotropic: The chains flatten on the surface. The resulting A- and B-lamellae have interfaces practically perpendicular to the walls, as also observed in recent experiments. Our simulations indicate the onset of long-range surface ordering before the bulk orders. The strongest effects take place between the spinodal and the order–disorder transition point of the diblock copolymer melt. © 1999 American Institute of Physics.
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  • 21
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    The Journal of Chemical Physics 111 (1999), S. 3733-3743 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: There is a variety of experimental evidence for lamellar-to-lamellar phase transitions in aqueous solutions of single- and two-component surfactant systems. We develop here the statistical thermodynamics of alternative scenarios for lamellar–lamellar coexistence. In one case the transition involves phase separation driven by demixing of the two amphiphiles within each bilayer; a purely repulsive interaction between bilayers is sufficient, because of its dependence on bilayer composition. In the complementary case, a condensation-type phase change is involved, caused by the competition between attractive and repulsive interactions; the primary order parameter for this transition is the overall surfactant concentration. © 1999 American Institute of Physics.
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  • 22
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    The Journal of Chemical Physics 111 (1999), S. 3753-3760 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The 46-bead, three-color model of a β-barrel-forming protein is modified by the addition of a single side group, represented by a bead which may be hydrophilic or hydrophobic. Molecular dynamics and quenching simulations show how the nature and location of the bead influence both the structure at the global minimum of internal energy and the relaxation processes by which the system finds its minima. The most drastic effects occur with a hydrophobic side group in the middle of a sequence of hydrophobes. © 1999 American Institute of Physics.
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  • 23
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    The Journal of Chemical Physics 111 (1999), S. 3744-3752 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this paper we complete the study of the phase diagram and conformational states of a stiff homopolymer. It is known that folding of a sufficiently stiff chain results in formation of a torus. We find that the phase diagram obtained from the Gaussian variational treatment actually contains not one, but several distinct toroidal states distinguished by the winding number. Such states are separated by first order transition curves terminating in critical points at low values of the stiffness. These findings are further supported by the off-lattice Monte Carlo simulation. Moreover, the simulation shows that the kinetics of folding of a stiff chain passes through various metastable states corresponding to hairpin conformations with abrupt U-turns. © 1999 American Institute of Physics.
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  • 24
    ISSN: 1089-7690
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    Topics: Physics , Chemistry and Pharmacology
    Notes: Gel-type electrolytes based on fluorinated polymers are of interest for electrochemical devices. We present a 7Li–13C solid-state NMR and modulated differential scanning calorimetry (MDSC) study of gel electrolytes based on a copolymer poly(vinylidene fluoride) (PVdF)–hexafluoropropylene (HFP) activated with a nonaqueous solution ethylene carbonate (EC)–propylene carbonate (PC)–LiN(CF3SO2)2. We show that the narrowing of the Li lineshape is decoupled from the glass transition. The behavior of the longitudinal relaxation times, T1, confirms that the host polymer matrix simply behaves like a quasiinert cage for the solution. These results are confirmed by 13C NMR at the magic angle (MAS) data, which show that the presence of the polymer does not significantly affect the chemical shift changes induced in the EC/PC carbons by the imide salt. © 1999 American Institute of Physics.
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  • 25
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    The Journal of Chemical Physics 111 (1999), S. 3769-3770 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We examine recently obtained expressions for the reversible work required to form a noncritical nucleus in a metastable vapor. We demonstrate that the expression obtained in by Debenedetti and Reiss [J. Chem. Phys. 108, 5498 (1998)] is identical to that in by Nishioka and Kusaka [J. Chem. Phys. 96, 5370 (1992)], thereby resolving the apparent contradiction between these two papers. © 1999 American Institute of Physics.
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  • 26
    ISSN: 1089-7690
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    Topics: Physics , Chemistry and Pharmacology
    Notes: External constraints are necessary in order to calculate the energetics of embryo formation when the embryo is not a critical nucleus. The expression for the reversible work of formation obtained in by Debenedetti and Reiss [J. Chem. Phys. 108, 5498 (1998)] is rigorous and valid regardless of the relative densities of the embryo and mother phase. © 1999 American Institute of Physics.
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  • 27
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    The Journal of Chemical Physics 111 (1999), S. 2853-2856 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We study the dynamics in optical collisions of Na with Ne, Ar, Kr, and Xe in a differential scattering experiment. We report the observation of nonadiabatic transitions in the excited collisional quasimolecule based on measurements of the population ratio of the Na(3p)2P1/2 and 2P3/2 fine-structure levels. Comparison with theoretical results shows a generally very good agreement over the range of collision energies (0.01–0.3 eV) scanned in our experiment, using the best available potentials. For the heavier rare-gas systems a strong influence of the BΣ–AΠ crossing on the population ratios is observed. We further extract a universal function for the nonadiabatic transition probability for these systems. In the thermal energy range, our results are in good qualitative agreement with data from gas phase optical collision experiments. © 1999 American Institute of Physics.
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  • 28
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The chemical dynamics to form cyanopropyne, CH3CCCN (X 1A1), and cyanoallene, H2CCCHCN (X 1A′), via the neutral–neutral reaction of the cyano radical, CN (X 2Σ+), with methylacetylene, CH3CCH (X 1A1), is investigated under single collision conditions in a crossed molecular beam experiment at a collision energy of 24.7 kJ mol−1. The laboratory angular distribution and time-of-flight spectra of the C4H3N products are recorded at m/e=65, 64, 63, and 62. The reaction of d3-methylacetylene, CD3CCH (X 1A1), with CN radicals yields reactive scattering signal at m/e=68 and m/e=67 demonstrating that two distinct H(D) atom loss channels are open. Forward-convolution fitting of the laboratory data reveal that the reaction dynamics are indirect and governed by an initial attack of the CN radical to the π electron density of the β carbon atom of the methylacetylene molecule to form a long lived CH3CCHCN collision complex. The latter decomposes via two channels, i.e., H atom loss from the CH3 group to yield cyanoallene, and H atom loss from the acetylenic carbon atom to form cyanopropyne. The explicit identification of the CN vs H exchange channel and two distinct product isomers cyanoallene and cyanopropyne strongly suggests the title reaction as a potential route to form these isomers in dark molecular clouds, the outflow of dying carbon stars, hot molecular cores, as well as the atmosphere of hydrocarbon rich planets and satellites such as the Saturnian moon Titan. © 1999 American Institute of Physics.
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  • 29
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The Cl− yield produced by dissociative electron attachment of a submonolayer of CF2Cl2 is enhanced by factors of 102 and 104 when CF2Cl2 is coadsorbed with water ice and ammonia ice, respectively, on a surface at ∼25 K. Moreover, the magnitude of Cl− enhancement increases strongly with decreasing CF2Cl2 concentration. This enhancement is attributed to dissociation of CF2Cl2 by capture of electrons self-trapped in polar water or ammonia molecules. This process may be an unrecognized sink for chlorofluorocarbons in the atmosphere. Cl− ions produced may be directly or indirectly converted to Cl atoms, which then destroy ozone. © 1999 American Institute of Physics.
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  • 30
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    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 2865-2868 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A structure-based tunneling mechanism developed to predict the ionization of molecules subjected to intense, ultrafast irradiation is tested on the series of C2 hydrocarbons: acetylene, ethylene, and ethane. Relative ionization probabilities (1, 4.1, and 8.7 for ethane, acetylene, and ethylene, respectively) are measured upon excitation with 780 nm, 125 fs pulses of 6×1013 W cm−2 and compared to predictions of the model (1, 4.1, and 7.9 for ethane, acetylene, and ethylene, respectively). Ionization probabilities determined via the ADK (Ammosov, Delone, and Krainov) model for atomic ionization (1, 2.7, and 13.1 for ethane, acetylene, and ethylene, respectively) are shown to be near those of the structure-based model. © 1999 American Institute of Physics.
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  • 31
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    The Journal of Chemical Physics 111 (1999), S. 2869-2877 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this paper, a methodology is introduced by which one may compute rates of nonadiabatic processes for arbitrary potential forms. This method augments the extant path-integral transition state theory approach in which information about the inherently dynamical rate process is obtained from a static analysis of a free energy surface. The present resulting formula reduces to previous single adiabatic surface results when the adiabatic surface are well separated. Numerical examples show that the method well approximates the exact results in the nonadiabatic limit and over a large range of temperatures for quadratic and for nonquadratic potentials. Corroborating these results, analysis of the rate formula for a single-oscillator spin-boson Hamiltonian in the nonadiabatic classical-limit reveals close agreement with the known exact result. © 1999 American Institute of Physics.
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  • 32
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    The Journal of Chemical Physics 111 (1999), S. 2889-2899 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We analyze the performance of a density functional model obtained by combining the Perdew–Burke–Erzenrhof (PBE) generalized gradient functional with a predetermined amount of exact exchange for predicting vertical electronic excitation energies within a time-dependent approach. Four molecules, namely, CO, H2CO, (CH3)2CO, and C2H4, have been chosen as benchmark cases. Our results show that this model (PBE0) provides accurate excitations both to valence and Rydberg states. Furthermore, the results are numerically close to those obtained using asymptotically correct exchange-correlation functionals. The performance of the PBE0 model for predicting excitation energies in larger molecules is assessed for benzene, pyridine, and naphthalene. Here, the PBE0 model provides results which are in fairly good agreement with experimental data and of similar quality to those obtained by more sophisticated (and time-consuming) post-Hartree–Fock methods. © 1999 American Institute of Physics.
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  • 33
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A time-dependent density-functional theory for systems in periodic external potentials in time is formulated on the assumption of the existence of the Floquet states from the quasienergy viewpoint. Coupling strength integration, which connects a noninteracting system with an interacting system, is introduced by using the time-dependent Hellmann–Feynman theorem. Coupled perturbed time-dependent Kohn–Sham equations are derived from the variational condition to the quasienergy functional with respect to parameters. Explicit expressions for frequency-dependent polarizability and first hyperpolarizability are given by the quasienergy derivative method. Excitation energies and transition moments are defined from poles and residues of frequency-dependent polarizabilities, respectively. In contrast to the previous theory, our formulation has the following three advantages: (1) The time-dependent exchange-correlation potential is defined by the functional derivative of the exchange-correlation quasienergy. (2) The formal expression for frequency-dependent polarizability, which corresponds to the exact sumover-states expression, can be obtained. (3) Explicit expressions for response properties which satisfy the 2n+1 rule can be automatically obtained. © 1999 American Institute of Physics.
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  • 34
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    The Journal of Chemical Physics 111 (1999), S. 2900-2909 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present analytical calculations of the electronic spin–orbit interaction contribution to nuclear magnetic shielding tensors using linear and quadratic response theory. The effects of the Fermi contact and the spin-dipole interactions with both the one- and two-electron spin–orbit Hamiltonians, included as first-order perturbations, are studied for the H2X (X=O, S, Se, and Te), HX (X=F, Cl, Br, and I), and CH3X (X=F, Cl, Br, and I) systems using nonrelativistic multiconfiguration self-consistent field reference states. We also present the first correlated study of the spin–orbit-induced contributions to shielding tensors arising from the magnetic field dependence of the spin–orbit Hamiltonian. While the terms usually considered are formally calculated using third-order perturbation theory, the magnetic-field dependent spin-orbit Hamiltonian requires a second-order calculation only. For the hydrogen chalcogenides, we show that contributions often neglected in studies of spin–orbit effects on nuclear shieldings, the spin-dipole coupling mechanism and the coupling of the two-electron spin–orbit Hamiltonian to the Fermi-contact operator, are important for the spin–orbit effect on the heavy-atom shielding, adding up to about half the value of the one-electron spin–orbit interaction with the Fermi-contact contribution. Whereas the second-order spin-orbit-induced shieldings of light ligands are small, the effect is larger for the heavy nuclei themselves and of opposite sign compared to the third-order contribution. © 1999 American Institute of Physics.
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  • 35
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    The Journal of Chemical Physics 111 (1999), S. 2910-2920 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Transformations among molecular orbitals are often expedient or illuminating, and sometimes essential in quantum chemical contexts. In order to express the many-electron wavefunction in terms of the corresponding transformed configurations, full CI calculations used to be repeated in the transformed orbital basis. The configurational transformations can however be obtained directly, as shown by Malmqvist, by a factorization into single orbital transformations. In the present paper, a direct transformation method is presented that is based on the factorization of orbital transformations in terms of Jacobi rotations. Compared to the repetition of a CI calculation, both direct re-expansion methods drastically reduce the computational effort and increase the numerical accuracy. They are, moreover, applicable to wavefunctions whose original construction is not accessible. © 1999 American Institute of Physics.
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  • 36
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    The Journal of Chemical Physics 111 (1999), S. 2921-2926 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have developed a database of 29 molecules for which we have estimated the complete-one-electron-basis-set limit of the zero-point-exclusive atomization energy for five levels of electronic structure theory: Hartree–Fock (HF) theory, Møller–Plesset second- and fourth-order perturbation theory, coupled cluster theory based on single and double excitations (CCSD), and CCSD plus a quasiperturbative treatment of triple excitations [CCSD(T)], all at a single set of standard geometries. Convergence checks indicate that the estimates are within a few tenths of a kcal/mol of the n=infinity limit of the cc-pVnZ basis set sequence. This data is then used to obtain optimized power-law exponents for extrapolating to the basis-set-limit from correlation-consistent polarized valence double and triple zeta (cc-pVDZ and cc-pVTZ) basis sets. This allows one to get thermochemical accuracy comparable to polarized quadruple or quintuple zeta (cc-pVQZ or cc-pV5Z) basis sets with a cost very comparable to polarized triple zeta, which is one order of magnitude less expensive than polarized quadruple zeta and two orders of magnitude less expensive than polarized quintuple zeta. © 1999 American Institute of Physics.
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  • 37
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    The Journal of Chemical Physics 111 (1999), S. 2927-2939 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A consistent treatment of environmental effects is proposed in the framework of the multiconfiguration time-dependent Hartree (MCTDH) method. The method is extended in view of treating complex molecular systems which require an exact quantum dynamics for a certain number of "primary" modes while an approximate dynamics is adequate for a class of "secondary" modes. The latter may correspond to the weakly coupled modes in a polyatomic molecule, or the first solvent shell in a solute-solvent complex. For these modes, a description in terms of parameterized functions is introduced. The MCTDH working equations are generalized to allow for the nonorthogonality of these functions, which may take, e.g., a multidimensional Gaussian form. The formalism is developed on the level of both the wave function description and the density matrix description. Dissipative effects are accounted for in terms of a stochastic Hamiltonian approach versus master equation approach in the respective descriptions. © 1999 American Institute of Physics.
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  • 38
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The structure and physical significance of the full set of solutions to coupled-cluster (CC) equations at various stages of the dissociation process and the impact of the choice of reference functions on these solutions have been studied for the first time. The equations for the CC method involving double excitations (CCD) are obtained for the P4 model consisting of two H2 molecules in a rectangular nuclear configuration determined by a geometry parameter α. We consider equations for the reference states |ΦA〉, |ΦQ〉, and |ΦB〉 corresponding to the lowest, highest, and intermediate Hartree–Fock (HF) energies, respectively. The first two states provide a size-consistent description of the dissociation process. For the compact-molecule geometries (α<10.0) the sets of complete solutions to the standard CCD equations [based on molecular orbitals (MOs) of D2h symmetry] in the spin–orbital and spin–symmetry-adapted versions always consist of 20 and 12 entries, respectively. For |ΦA〉 and |ΦB〉 in the dissociation limit (α→∞) only for the latter version the solutions can be attained by homotopy method. In this case we have reformulated the standard spin–symmetry-adapted CCD equations to a version based on the use of localized orbitals (LO) which is extremely simple and can be solved analytically providing an understanding of the unexpected peculiarities of the solutions for α→∞. For |ΦA〉 and |ΦQ〉, there are only two regular solutions. For the remaining 10 solutions, the CCD wave functions are meaningless despite the fact that the corresponding CCD energies are equal to the exact values. © 1999 American Institute of Physics.
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  • 39
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The impact of approximations to the form of the cluster operator on the structure and physical significance of the complete set of geometrically isolated solutions to the coupled-cluster (CC) equations has been studied for the first time. To systematically study the correspondence of solutions obtained at various levels of the approximation process, a continuation procedure based on a set of β-nested equations (β-NE) has been proposed and applied. Numerical studies based on a homotopy method for obtaining full solutions to sets of polynomial equations have been performed for the H4 and P4 models which belong to the simplest realistic many-electron model systems. Two examples of approximation procedures have been considered. The first one involved, for the P4 model, the approximation leading from the full CC (FCC) method to the CC method based on double excitations (CCD). As a result of this approximations the number of solutions has increased from 8 to 20. In the second example, for H4, we have studied the approximation leading from the CCSD method to the CCD one. To complete these studies, we have for the first time obtained the full set of geometrically isolated solutions for a CCSD equations which consists of 60 solutions. Only a small subset of this set might have some physical significance. During the approximation process considered, the number of solution decreases from 60 to 12. This radical drop of the numbers of solutions is a consequence of the absence of the third and fourth powers of the unknowns in the CCD equations. © 1999 American Institute of Physics.
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  • 40
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    The Journal of Chemical Physics 111 (1999), S. 2960-2967 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Fourier transform spectroscopic measurements of the absorption bands of the Herzberg II (c 1Σu−–X 3Σg−) of O2 at 295 K have been made with a resolution of 0.06 cm−1 in the wavelength region 240–275 nm. Rotational line positions are determined with an accuracy of 0.005 cm−1, and rotational term values are presented for the vibrational levels, v′=6–16. Precise band oscillator strengths of the (7,0)–(16,0) bands are obtained for the first time by direct measurement by summing the cross sections of individual rotational lines of the bands. The rotational line strengths and the branching ratios are also presented for the same bands. © 1999 American Institute of Physics.
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  • 41
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    The Journal of Chemical Physics 111 (1999), S. 2968-2972 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In previous experiments, a nearly complete vibrational spectrum of the CS2 molecule in the Σg+ state has been obtained using a laser induced fluorescence method. The statistical tests of the random matrix theory, applied on this spectrum, suggest a transition to quantum chaos. The aim of this letter is to show that these statistical results are biased because of a nonsingle excitation of the molecule. This is experimentally confirmed by high-resolution new experiments in supersonic jet, using the powerful laser chain of the french project for the isotopic separation of uranium by laser (SILVA project). © 1999 American Institute of Physics.
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  • 42
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    The Journal of Chemical Physics 111 (1999), S. 2973-2977 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Potential energy curves and spectroscopic parameters of the ground and exited states of SiCu, SiCu+, and SiCu− are presented. The calculations were performed by high-level correlated methods including the relativistic correction for the lowest states. The present results are compared with recent theoretical and experimental studies of SiCu and its ions and support the earlier theoretical conclusions concerning the assignment of the electronic ground state of SiCu. According to calculations presented in this paper the lowest energy states of SiCu, SiCu+, and SiCu−, are 2Πr, 1Σ+, and 3Σ−, respectively. © 1999 American Institute of Physics.
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  • 43
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    The Journal of Chemical Physics 111 (1999), S. 2978-2984 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Employing molecular beam depletion spectroscopy and Fourier transform infrared matrix spectroscopy, respectively, we have studied the O–H stretching vibrations of the glycine conformers I, II, and III. The glycine molecules were either deposited into large liquid helium clusters HeN, N¯=11000, THe=0.4 K) or trapped in various rare gas matrices (Ne, Ar, Kr) at temperatures below 12 K. By extrapolating the experimental data plotted as a function of the square root of the critical temperature of the matrix material, the positions of the gas phase absorption bands were estimated to be 3585±2 cm−1 (conformer I), 3295±3 cm−1 (conformer II), and 3580±5 cm−1 (conformer III). The experimental results are compared with recent ab initio calculations. © 1999 American Institute of Physics.
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  • 44
    ISSN: 1089-7690
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    Topics: Physics , Chemistry and Pharmacology
    Notes: (1+1′) resonance enhanced multiphoton ionization (REMPI) spectra of jet-cooled KrXe and ArXe in the vicinity of the high energy Xe*5d[3/2]10←Xe(1S0) atomic line at 83889.99 cm−1 were obtained by exciting the neutral dimers with tunable coherent vacuum ultraviolet (VUV) radiation generated by four-wave sum mixing in mercury vapor, and then detecting the resultant ions in a time-of-flight (TOF) mass spectrometer. Precise excited state constants were derived from analyses of the resultant vibrational fine structure, while equilibrium bond lengths were estimated from Franck–Condon factor intensity simulations. Excited state symmetries were deduced from separate ultraviolet (UV) (2+1) REMPI spectra recorded with linearly and circularly polarized light. The results of this work confirm a recent model proposed by Lipson and Field, where the RgXe*(5d) states are predicted to be strongly destabilized relative to RgXe*(6p) due to strong 5d-6p Xe* l-mixing induced by the ground state Rg atom partner making up the dimer. Orbital mixing is also responsible for the observation of appreciably strong RgXe*(5d) spectra in both one- and two-photon excitation. © 1999 American Institute of Physics.
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  • 45
    ISSN: 1089-7690
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    Topics: Physics , Chemistry and Pharmacology
    Notes: The photodissociation dynamics of gas phase I3− following 390 nm excitation are studied using femtosecond photoelectron spectroscopy. Both I− and I2− photofragments are observed; the I2− exhibits coherent oscillations with a period of 550 fs corresponding to ∼0.70 eV of vibrational excitation. The oscillations dephase by 4 ps and rephase at 45 and 90.5 ps on the anharmonic I2− potential. The gas phase frequency of ground state I3− is determined from oscillations in the photoelectron spectrum induced by resonance impulsive stimulated Raman scattering. The dynamics of this reaction are modeled using one- and two-dimensional wave packet simulations from which we attribute the formation of I− to three-body dissociation along the symmetric stretching coordinate of the excited anion potential. The photodissociation dynamics of gas phase I3− differ considerably from those observed previously in solution both in terms of the I2− vibrational distribution and the production of I−. © 1999 American Institute of Physics.
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  • 46
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    The Journal of Chemical Physics 111 (1999), S. 3004-3011 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The (H2O...HCl)− anion has been studied at the coupled cluster level of theory with single, double, and noniterative, triple excitations whereas lowest energy structures have been determined at the second-order Møller–Plesset level. The vertical electron detachment energy and the adiabatic electron affinity were found to be 475 and 447 cm−1, respectively, and they agree very well with the maximum of the dominant peak in the photoelectron spectrum of (H2O...HCl)− at 436 cm−1, recorded by Bowen and collaborators. Our results indicate that electron correlation contributions to the electron binding energy are important and represent ∼70% of its total value. Both for the neutral and the anion, the two equivalent Cs symmetry minima are separated by a C2v transition state and the energy barrier amounts to only 77 cm−1. Thus the equilibrium structures averaged over vibrations are effectively planar (C2v). The Franck–Condon (FC) factors, calculated in harmonic approximation, indicate that the neutral complex formed in photoelectron spectroscopy (PES) experiments may be vibrationally excited in both soft intermolecular and stiff intramolecular modes. The theoretical photoelectron spectrum based on the calculated FC factors is compared to the experimental PES spectrum of Bowen et al. © 1999 American Institute of Physics.
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  • 47
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    The Journal of Chemical Physics 111 (1999), S. 3012-3017 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The microwave spectra of P14N16O and its isotopomers P15N16O and P14N18O were observed in a dc glow discharge plasma of a mixture of nitric oxide and hydrogen gases over solid red phosphorus placed on the stainless steel electrode. Rotational transitions of the parent P14N16O species were measured in the ground state as well as in the vibrationally excited ν1 (PN str.), ν2 (bend), and 2ν2 states. The l=0 substate of the 2ν2 state interacts with the ν1 state through a Fermi resonance. The rotational constants determined for the ground states of the three isotopomers yield the substitution structure, rs(PN)=151.6516(87) pm and rs(NO)=119.5025(80) pm. © 1999 American Institute of Physics.
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  • 48
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    The Journal of Chemical Physics 111 (1999), S. 3018-3026 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An internal coordinate Hamiltonian model has been constructed to model torsional motion in the OH stretching vibrational overtone region of methanol, CH3OH. The model includes harmonic couplings between OH and CH stretching vibrations and Fermi resonance interactions between OH stretches and COH bends and between CH stretches and CH2 bends. A symmetrized basis set has been used to form block diagonal Hamiltonian matrices with strong resonance couplings off-diagonal. Observed torsional levels of the excited vibrational states have been used as data in a least squares optimization of the model parameters, some of which have been estimated by ab initio calculations. The experimentally observed increase in the effective torsional barrier in moving to highly excited OH stretching states has been explained by the model. © 1999 American Institute of Physics.
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  • 49
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    The Journal of Chemical Physics 111 (1999), S. 3027-3034 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Second-order Möller-Plesset perturbation theory (MP2) and density functional theory (DFT) were employed to optimize two cyclic conformations of the methanol trimer, denoted "bowl" and "chair," as well as a third noncyclic, "open-chain" conformation. This is the first time all three methanol trimer conformations have been studied at the same level of theory. Harmonic vibrational frequencies confirm that all stationary points are minima on the intermolecular potential energy hypersurface. The chair is consistently predicted to be the most stable conformer. The bowl and open-chain conformers are only slightly less stable and lie within 3 kcal/mol. Results indicate that the bowl structure contains a threefold rotational axis of symmetry which resolves a discrepancy over its symmetry in previous theoretical investigations. Further, this finding precludes the possibility that only the cyclic conformers of (CH3OH)3 are the source of the five bands observed in the OH stretching spectrum of the methanol trimer recently obtained by infrared cavity ringdown laser absorption spectroscopy. From the ab initio frequencies, it is concluded that the bowl, chair, and open-chain conformations of (CH3OH)3 must be present in the supersonic expansion in order to account for all five observed bands. © 1999 American Institute of Physics.
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  • 50
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    The Journal of Chemical Physics 111 (1999), S. 3035-3041 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The structure of two metal phthalocyanines, MPc where M=Sn and Mg, have been determined by gas-phase electron diffraction for the first time; furthermore, the structure of ZnPc established earlier by the same technique has been reanalyzed. The focus of these studies is the position of the metal ion relative to the 16-membered C8N8 ring. Tin(II)phthalocyanine we find to be nonplanar with the Sn(II) ion 1.0(1) Å above the molecular plane in accordance with its structure in crystal established earlier; the two other molecules were found to be planar. Slight nonplanarity of ZnPc found in the previous study is now removed by a new procedure of structural analysis; this is in accordance with the results of ab initio/DFT calculations for this molecule performed by Pulay. From comparisons presented here we can conclude that there is a close structural similarity of metal phthalocyanines in the gas phase and in crystal. © 1999 American Institute of Physics.
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  • 51
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    The Journal of Chemical Physics 111 (1999), S. 3051-3057 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The nuclear wave packet dynamics in the potential well of a bound molecule can be controlled by an intense infrared (IR)-laser pulse. The phase of the nuclear wave packet motion is shown to depend on the phase of the laser field and the initial orientation of the molecule. We demonstrate, for diatomic heteronuclear molecules, that these spatial effects can be used to control the angular distribution of photofragments by selective dissociation of molecules with a given initial orientation from a sample of randomly oriented molecules. © 1999 American Institute of Physics.
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  • 52
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    The Journal of Chemical Physics 111 (1999), S. 3874-3879 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Rotational transitions with high quantum numbers J and K of the 1:1 complex of benzonitrile with H2O and D2O have been investigated in the frequency range 60–78 GHz with the free jet absorption microwave technique to get detailed information on the unusual hydrogen bond and on the dynamics of the large amplitude motions of the water moiety. With respect to previous microwave studies [V. Storm, D. Consalvo, and H. Dreizler, Z. Naturforsch. A 52, 293 (1997); R. M. Helm, H.-P. Vogel, H. J. Neusser, V. Storm, D. Consalvo, and H. Dreizler, 52, 655 (1997); V. Storm, H. Dreizler, and D. Consalvo, Chem. Phys. 239, 109 (1998)] the position of the water oxygen has been confirmed and the planar configuration of the complex has been determined. The distance of the oxygen atom to the ortho hydrogen is 2.48 Å, the angle to the ortho C–H bond is 144° and the angle between the free hydrogen atom of water with the same C–H bond is 164°. A coupled analysis of the 0+ and 0− states observed for the normal species was performed and the experimental data were reproduced by a flexible model which allowed the determination of the barrier to internal rotation of water [V2=287(20) cm−1] and the structural relaxation associated with the dynamic process. © 1999 American Institute of Physics.
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  • 53
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Photoionization thresholds for Gen (n≤57) and Snn (n≤41) are examined by laser photoionization with detection by reflectron time-of-flight mass spectrometry. Stimulated Raman anti-Stokes scattering of narrow bandwidth 193, 248, and 266 nm radiation is used to produce ionization light sources in the vacuum ultraviolet region (200–141 nm). A very similar size dependence of the ionization potentials (IPs) is found for germanium and tin clusters with fewer than 12 atoms, featuring a major maximum at n=10. The rather high IP of Ge10 compared with its neighbors is consistent with the results of a photodissociation study of Gen+. We also find a rapid decrease in the IPs for Gen between n=15 and 26, which is very similar to that for silicon clusters reported in our previous paper. On the other hand, the IPs of medium size Snn (n=15–41) clusters are found to decrease slowly without such a gap. The remarkable difference in the size dependence of the IPs for the Sin, Gen, and Snn clusters is discussed in relation to the existence of a structural transition in the medium-size Sin and Gen clusters. © 1999 American Institute of Physics.
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  • 54
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    The Journal of Chemical Physics 111 (1999), S. 3891-3897 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Rate constants for vibrational energy exchange in CO collisions have been calculated for normal CO and two isomers. The calculations have been carried out using a semiclassical collision model in which translational and rotational motions are treated classically. The vibrational degrees of freedom are quantized. The theoretical predicted rates agree well with recent experimental data. © 1999 American Institute of Physics.
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  • 55
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    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 3898-3910 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The S0↔S1 electronic transition of 1H-indazole has been investigated by laser-induced fluorescence (LIF) excitation and dispersed fluorescence (DF) spectroscopies in a supersonic free jet expansion. Ground and excited state vibrational modes were assigned based on the observed band frequencies and intensities, ab-initio frequency calculations, and available infrared absorption data. Unexpected "symmetry forbidden" transitions were observed in the DF, which, according to our assignments, would originate from the 271 excited state in-plane fundamental to several ground state out-of-plane fundamentals. Accepting the assignments, this observation would indicate a vibronic coupling between the S1 (or S0) state (A′) and an excited nπ*-type electronic state of A″ symmetry. © 1999 American Institute of Physics.
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  • 56
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    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 3911-3918 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Rhomboidal SiC3, a planar ring with C2v symmetry and a transannular C–C bond, was detected at centimeter wavelengths in a pulsed supersonic molecular beam with a Fourier transform microwave (FTM) spectrometer, and was subsequently observed in a low-pressure dc glow discharge with a free-space millimeter-wave absorption spectrometer. The rotational spectrum of SiC3 is characterized by large harmonic defects and large splitting of the K-type doublets. Lines in the centimeter-wave band were very strong, allowing the singly substituted isotopic species to be observed in natural abundance. Measurements of the normal and five isotopically substituted species with the FTM spectrometer provided conclusive evidence for the identification and yielded an experimental zero-point (r0) structure. Forty-six transitions between 11 and 286 GHz with Ka≤6 were measured in the main isotopic species. Three rotational and nine centrifugal distortion constants in Watson's A-reduced Hamiltonian reproduce the observed spectrum to within a few parts in 107 and allow the most intense transitions up to 300 GHz to be calculated with high accuracy. The spectroscopic constants confirm that SiC3 is a fairly rigid molecule: the inertial defect is comparable to those of well-known planar rings and the centrifugal distortion constants are comparable to molecules of similar size. The number of SiC3 molecules in our supersonic molecular beam in each gas pulse is at least 3×1011, so large that electronic transitions may be readily detectable by laser spectroscopy. © 1999 American Institute of Physics.
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  • 57
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A pulsed molecular beam cavity Fourier transform microwave spectrometer was used to measure pure rotational spectra of nine isotopomers of Ne2–N2O, and of three isotopomers of the Ar2–N2O van der Waals trimer. For Ne2–N2O, these are 20Ne20Ne–14N14N16O, 20Ne22Ne–14N14N16O, 22Ne22Ne–14N14N16O, 20Ne20Ne–15N14N16O, 20Ne22Ne–15N14N16O, 22Ne22Ne–15N14N16O, 20Ne20Ne–14N15N16O, 20Ne22Ne–14N15N16O, and 22Ne22Ne–14N15N16O. Those for Ar2–N2O are 40Ar40Ar–14N14N16O, 40Ar40Ar–15N14N16O, and 40Ar40Ar–14N15N16O. The spectra were measured in the frequency range between 3 and 18 GHz. Both a- and c-type transitions were measured for all Ne2–N2O isotopomers. In the case of the mixed, 20Ne22Ne containing, isotopomers a small b-dipole moment occurs and two b-type transitions were measured. In the spectra of Ar2–N2O only b- and c-type transitions were measured. Rotational and centrifugal distortion constants were determined for all the isotopomers of each complex. The spectral analyses show that Ne2–N2O is a highly asymmetric prolate rotor (κ=−0.158 for 20Ne20Ne–14N14N16O) while Ar2–N2O is a highly asymmetric oblate rotor (κ=0.285 for 40Ar40Ar–14N14N16O). Both trimers were found to have distorted tetrahedral structures with the rare gases tilted towards the O atom of the N2O subunit. Nuclear quadrupole hyperfine structures due to both terminal and central 14N nuclei were observed and analyzed to give the nuclear quadrupole coupling constants, χaa(1), χbb(1) and χaa(2), χbb(2). The resulting spectroscopic constants were utilized to derive ground state effective structures, ground state average structures, and partial substitution structures. Harmonic force field analyses were performed for each complex using the obtained quartic centrifugal distortion constants. The results of the spectroscopic analyses are discussed in the light of possible three-body nonadditive interactions. © 1999 American Institute of Physics.
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  • 58
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    The Journal of Chemical Physics 111 (1999), S. 3929-3939 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this paper, we present detailed quantum treatment of the semirigid vibrating rotor target (SVRT) model for reaction dynamics involving polyatomic molecules. In the SVRT model, the reacting (target) molecule is treated as a semirigid vibrating rotor which can be considered as a three-dimensional generalization of the diatomic molecule. This model provides a realistic framework to treat reaction dynamics of polyatomic systems. Using the SVRT model, it becomes computationally practical to carry out quantitatively accurate quantum dynamics calculation for a variety of dynamics problems in which the reacting molecule is a polyatomic or complex molecule. In this work, specific theoretical treatment and mathematical formulation of the SVRT model are presented for three general classes of reaction systems: (1) reaction of an atom with a polyatomic molecule (atom–polyatom reaction), (2) reaction between two polyatomic molecules (polyatom–polyatom reaction), and (3) polyatomic reaction with a rigid surface (polyatom–surface reaction). Since the number of dynamical degrees of freedom in the SVRT model for the above three classes of dynamical problems is limited, accurate quantum (both ab initio and dynamical) calculations are possible for many reactions of practical chemical interest. In this paper, a time-dependent wave packet approach is employed to implement the SVRT model for dynamics calculation of polyatomic reactions. © 1999 American Institute of Physics.
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  • 59
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Photodissociation of the H2S molecule at 157.6 nm was studied experimentally using the Rydberg tagging technique. Translational energy distributions of the H-atom product from the H2S photodissociation were measured, and the SH(X 2Π)+H(2S) channel was found to be the dominant dissociation process. Spin-orbit and rovibrational state distributions were also obtained for the SH product, which was found to be both vibrationally and rotationally excited. An intriguing bimodal rotational distribution in the lowest two vibrational states, v=0 and 1, has been clearly observed for the SH product, indicating that there are two distinctive dissociation mechanisms involved in the photodissociation of H2S at 157 nm excitation. © 1999 American Institute of Physics.
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  • 60
    ISSN: 1089-7690
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    Topics: Physics , Chemistry and Pharmacology
    Notes: Rotationally resolved S1←S0 electronic spectra of the van der Waals complexes indole-Ar and N-deuterated-indole-Ar in the gas phase are described. Both spectra exhibit inertial axis reorientation. A comparison of the parameters derived from fits of the two spectra with those obtained from a previous study of the bare molecule [Berden et al., J. Chem. Phys. 103, 9596 (1995)] shows that the Ar atom in indole-Ar is attached above the indole plane, displaced toward the N atom in the five-membered ring, in both electronic states. However, the measured center-of-mass coordinates of the Ar atom in the principal axis frames of indole in the two states are different, leading to the observed axis reorientation in the high resolution spectra. The S1 state in indole itself is shown to be the 1Lb state, which has a different electronic distribution from that of the ground state. Thus, the Ar atom "moves" when the photon is absorbed because there are significant differences in the intermolecular potential energy surfaces of the two states. © 1999 American Institute of Physics.
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  • 61
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The guided-ion beam method has been used to measure time-of-flight (TOF) spectra of the NO+ produced in the reaction of O+(4S) and N2(X 1Σg+). Particular care was taken to minimize the participation of the O+(2D,2P) metastables in the reactions, the success of which is validated by measuring the absolute cross section for the reaction as a function of collision energy in the near-thermal to 1.5 eV range. In this range, the cross section exhibits a region of low reactivity at near-thermal energies, which can be obscured by reactions of metastables and other effects, and a region of sharply increasing reactivity above a threshold of collision energy (approximate)0.3 eV. The velocity-transformed TOF spectra, at collision energies of 0.51 eV, 0.80 eV, 3.2 eV, and 6.3 eV, indicate two reaction mechanisms: in the first, product ions are scattered backward with inefficient translational to internal energy conversion; in the second, product ions arise from intermediate collision complexes with efficient translational energy conversion. The first mechanism is associated with the passage through the spin-forbidden doublet ground state N2O+ intermediate, while the second involves passage through an endothermic quartet intermediate. © 1999 American Institute of Physics.
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  • 62
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The coupling of two large amplitude motions, the internal rotation of the methyl group and the intramolecular proton transfer, has been investigated for jet-cooled 5-methyltropolone, 5-methyltropolone–OD, and the 5-methyltropolone–(H2O)1 1:1 hydrogen-bonded complex by measuring the fluorescence excitation, dispersed fluorescence, and hole-burning spectra in the S1–S0 region. The vibronic bands in the excitation spectrum of 5-methyltropolone consist of four components originating from the transitions between the sublevels in the S1 and S0 states. The intensity of the bands, the frequencies, and the change in the stable conformation of the methyl group upon photoexcitation have been analyzed for 5-methyltropolone–(H2O)1 by calculating the one-dimensional periodic potential function, which provides the correlation between the internal rotational levels of 5-methyltropolone–(H2O)1 and the sublevels of 5-methyltropolone. It has been shown that the electronic transitions between the sublevels within the same symmetry are allowed in 5-methyltropolone. The tunneling splitting of the zero-point level in the S1 state is 2.2 cm−1 for 5-methyltropolone. The corresponding splitting for 5-methyltropolone–OD is less than 0.5 cm−1. A drastic decrease of the tunneling splitting for 5-methyltropolone as compared to that for tropolone (19.9 cm−1) is ascribed to a strong coupling between the two large amplitude motions in the S1 state. The existence of a similar coupling has been suggested in the S0 state of 5-methyltropolone. The excitation of the sublevel in the S1 state considerably promotes proton tunneling. This effect has been explained by the delocalization of the wave function of the internal rotation of the methyl group. The two-dimensional potential energy surface along the proton transfer coordinate and the rotational angle of the methyl group has been calculated to explain the effects of the coupling on proton tunneling. © 1999 American Institute of Physics.
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  • 63
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The infrared spectrum of the iron dicarbonyl radical Fe(CO)2 produced in a supersonic jet expansion by the excimer laser photolysis of iron pentacarbonyl Fe(CO)5 was observed by time-resolved infrared diode laser spectroscopy. About 170 transitions, each split into one or two fine structure components, were assigned to the ν3 (CO antisymmetric stretch) band of Fe(CO)2. The assignment was greatly facilitated by spectral simplification caused by rotational as well as vibrational cooling in the supersonic jet. It was observed that lines are missing at alternate J quantum numbers in each spin component, which confirmed that Fe(CO)2 is a linear molecule with D∞h symmetry and that the electronic ground state is of 3Σg− symmetry. The rotational and centrifugal distortion constants in the ground state were determined to be B0=1414.675(46) MHz and D0=0.3077(74) kHz, respectively. The spin–spin interaction constants obtained, λ0=655.3(42) GHz, is comparable with that of the FeCO radical, λ0=684.470(51) GHz. The ν3 band origin was determined to be 1928.184335 (82) cm−1. The figures in parentheses are uncertainties (1σ) in units of the last digit. © 1999 American Institute of Physics.
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  • 64
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    The Journal of Chemical Physics 111 (1999), S. 3978-3988 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: High level ab initio (G2MS and CASSCF) and density functional (B3LYP) calculations were carried out to study the mechanism of the ion–molecule reaction C2H2++CH3OH for four reaction channels: hydride abstraction from methanol (HA), proton transfer from acetylene cation (PT), charge transfer (CT), and covalent complex formation (CC) channel. For the CT channel, two pathways have been found: a usual nonadiabatic pathway via A′/A″ seam of crossing, and a low-energy adiabatic pathway through an initial intermediate; the latter may be the dominant process with favorable energies and a large impact parameter. The HA process involves a low-energy direct intermediate and a very low barrier to form C2H3+CH2OH+ and is also energetically favorable. The PT processes require passage over a high-energy transition state (TS) and are not important. One of the experimentally unobserved CC channels, formation of the COCC skeleton, is energetically favorable and there is no energetic reason for it not to take place; a "dynamic bottleneck" argument may have to be invoked to explain the experiment. The increase in reaction efficiency with the C–C stretch excitation may be justified by considering the TSs for two CT pathways, where the C–C distance changed substantially from that in the reactant C2H2+. Very qualitatively, the C2H2++CH3OH potential energy surface looks more like that of the C2H2++NH3 system than the C2H2++CH4 system, because of the differences in the ionization potentials: NH3∼CH3OH<C2H2<CH4. © 1999 American Institute of Physics.
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  • 65
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    The Journal of Chemical Physics 111 (1999), S. 3989-3994 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Low-lying electronic states of TiCl and ZrCl were investigated by the complete active space SCF (CASSCF), multi-reference singly and doubly excited configuration interaction (MRSDCI), and multi-reference coupled pair approximation (MRCPA) calculations using the model core potential (MCP) method. Relativistic effects were incorporated in the MCP and basis sets for Zr at the level of Cowan and Griffin's quasi-relativistic Hartree–Fock method. The 4Φ state was found to be the ground state of TiCl, whereas the 2Δ state was the ground state of ZrCl at all levels of calculation. Two low-lying excited states were very close in energy to the ground state. The excited 4Σ− and 2Δ states of TiCl were higher than the ground state by 0.102 eV and 0.458 eV, respectively, and the excited 4Φ and 4Σ− states of ZrCl were higher by 0.094 eV and 0.110 eV, respectively, at the MRCPA level. The calculated values of re(2.319 Å) and ωe(382 cm−1) for the ground 4Φ state of TiCl are quite close to the values of re(2.351 Å) and ωe(383 cm−1) for the ground 2Δ state of ZrCl. The values of re, ωe, Be, and αe are reasonably comparable to the observed values for both TiCl and ZrCl. © 1999 American Institute of Physics.
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  • 66
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    The Journal of Chemical Physics 111 (1999), S. 4005-4012 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The photodissociation dynamics of CBrCl3 was studied near 234 and 265 nm using a two-dimensional photofragment ion imaging technique. Bromine fragments monitored in this study were produced via direct dissociation of CBrCl3, represented by CBrCl3→CCl3+Br(2P1/2)/Br(2P3/2). The branching ratio of Br(2P1/2) (denoted Br*)/Br(2P3/2) (denoted Br) showed strong excitation energy dependence. The product quantum yields at two different excitation wavelengths were Φ 234 nm(Br*)=0.31±0.01 and Φ 265 nm(Br*)=0.68±0.02, respectively. The speed and angular distributions of Br* and Br fragments were determined. Similar values of β(234 nm)=−0.44 and β(265 nm)=−0.47 for Br were observed, while β values for Br* were found to be markedly different, β(234 nm)=−0.34 and β(265 nm)=1.43. The strong curve crossing, 1Q1→3Q0, and the angular distribution of Br* suggesting a typical perpendicular transition, were observed at 234 nm photodissociation.© 1999 American Institute of Physics.
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  • 67
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    The Journal of Chemical Physics 111 (1999), S. 3042-3050 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report calculations, using electron uncorrelated and correlated wave functions, of the electronic and vibrational properties which pertain to certain nonlinear optical properties for HF, HCl, and HBr. Our main focus is on vibrational effects (zero-point-vibrational averaging and pure vibration). Analysis of the results obtained at various levels of approximation indicates that first-order perturbation theory is generally adequate for finding the zero-point-vibrational-averaging corrections for these molecules and that complete second-order perturbation theory nearly always gives reliable results for the pure vibrational corrections. Attention is drawn to some differences with previously published results for these properties. © 1999 American Institute of Physics.
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  • 68
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    The Journal of Chemical Physics 111 (1999), S. 3058-3069 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have obtained rotationally resolved pulsed filed ionization photoelectron (PFI-PE) spectra of NO in the energy range of 9.2–16.8 eV, covering ionization transitions of NO+(X 1Σ+,v+=0–32,J+)←NO(X 2Π3/2,1/2,v″=0,J″). The PFI-PE bands for NO+(X 1Σ+,v+=6–32) obtained here represent the first rotationally resolved spectroscopic data for these states. The simulation using the Buckingham–Orr–Sichel model provides accurate molecular constants for NO+(X 1Σ+,v+=0–32), including ionization energies, vibrational constants (ωe+=2 382.997±0.122 cm−1, ωe+χe+=17.437 84±0.000 90 cm−1, ωe+ye+=0.063 209 5±3.2×10−6 cm−1, and ωe+ze+=−0.001 400 0±7.2×10−8 cm−1), and rotational constants (Be+=1.996 608±0.006 259 cm−1, αe+=0.020 103±6.3×10−5 cm−1, and γe+=−(7.22±2.26)×10−6 cm−1). For v+=0–15, the rotational branches are ΔJ=J+−J″=±1/2, ±3/2, ±5/2, ±7/2, and ±9/2, which correspond to the formation of photoelectron angular momentum states l=0, 1, 2, and 3. The ΔJ=±1/2, ±3/2, ±5/2, ±7/2, ±9/2, and ±11/2 rotational branches are observed in the spectra for v+=16–32, revealing the production of continuum photoelectron states l=0, 1, 2, 3, and 4. The maximum ΔJ value and intensities for high ΔJ rotational branches are found to generally increase as v+ is increased in the range of 0–32. This observation is attributed to an increase in inelastic cross sections for collisions between the outgoing photoelectron and the nonspherical molecular ion core as the bond distance for NO+ is increased. Thus, this observation can be taken as strong support for the electron-molecular-ion-core scattering model for angular momentum and energy exchanges in the threshold photoionization of NO. © 1999 American Institute of Physics.
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  • 69
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    The Journal of Chemical Physics 111 (1999), S. 3070-3076 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: For the open shell van der Waals molecule, CAr, the potential energy curves (PECs) for the B 3Π and 1 5Σ− states, the B 3Π–1 5Σ− spin–orbit coupling and the B 3Π fine structure splitting are determined using multireference configuration interaction wave functions as large as ∼8 million configuration state functions. The B 3Π state is strongly bound, with De=5100 cm−1. Re(B 3Π)=3.7a0 and is considerably shorter than Re(X 3Σ−)=6.07 a0. The PEC for the repulsive 1 5Σ− state crosses that of the B 3Π state at Rx(1 5Σ−,B 3Π)=3.31a0 leading to spin–orbit induced predissociation. The B 3Π–1 5Σ− spin–orbit coupling is the result of valence-Ryberg mixing in the B 3Π state and is considerably enhanced by the heavy atom effect. The heavy atom effect is also reflected in a marked decrease in the fine structure splitting of the B 3Π state with increasing vibrational level. The implications of these results for using CAr(B 3Π) in laser induced fluorescence detection of CAr(X 3Σ−,v) are discussed. © 1999 American Institute of Physics.
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  • 70
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    The Journal of Chemical Physics 111 (1999), S. 3077-3082 
    ISSN: 1089-7690
    Source: AIP Digital Archive