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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 3739-3744 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Diamond powders with grain diameters up to 0.3 μm were obtained by CO2 -laser-induced decomposition of C2H4 at low pressures and temperatures. C2H4 or mixtures of C2H4, H2, and SiH4 were irradiated in a gas-flow reactor with the 10P14 line (10.532 μm) of a grating-tunable CO2 laser with 50-W cw output power. Solid products were produced in a yellow-to-orange colored flame (500–550 °C) and collected in filters. The product contained polyaromatic species, high molecular polymers, graphite, amorphous carbon, and spherical diamond particles. Several diamond particle populations, with mean diameters of 6–120 nm, were observed by transmission electron microscopy. Both diamond modifications, cubic and hexagonal, were identified by electron diffraction. Diamond formation is dependent on the residence time in the reaction flame, but relatively independent of the reactant gas compositions. Hydrogen-free pyrolysis of pure ethylene produced diamond of high purity (no diffraction rings of graphite detectable).
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 2582-2595 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The structures, binding energies, and vibrational frequencies of fully optimized water clusters (H2O)n, n=1– 4, were computed with ab initio molecular orbital theory at the SCF level using different basis sets. The SCF procedure allows satisfactory predictions for these properties compared with experimental results. For quantitative predictions of binding energies and geometrical parameters, a basis set including polarization functions is needed. With respect to intramolecular vibrational frequencies and frequency shifts, however, the split valence basis set 4-31G leads in all cases to the best rationalization of the available experimental data. Analysis of intramolecular force constants, frequencies, and eigenvectors for n=2 to 4 shows that (i) a transition from highly localized (n=2) to highly delocalized (n=4) vibrational modes takes place; (ii) the delocalized O–H vibrations of cyclic (H2O)n clusters (n≥3) can be described as longitudinal/transverse optical phonons; (iii) internal force constants for the hydrogen bonding O–H stretch, k(O–Hb), decrease strongly with size, leading to a decrease in the νbridge O–H frequencies; a similar decrease is found for the intramolecular bending force constant k(aitch-theta); (iv) force constants for the free O–H stretching motions k(O–Hf) stay nearly constant, as do the corresponding vibrational frequencies; (v) intermolecular stretch–stretch couplings increase substantially with n and dominate over intramolecular stretch–stretch couplings for n≥3; similarly, intermolecular bend–libration couplings are very important.
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 3751-3753 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 506-510 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The optical absorption spectra of the B˜ 2Π3/2 ← X˜ 2Π3/2 transitions of chloro-, bromo-, and iodocyanide cations in neon matrices at 4.5 K have been obtained and vibrationally analyzed. The origin band of the A˜ 2Σ+ ← X˜ 2Π3/2 transition of ICN+ is also observed as well as the absorption bands of the CN radical in the spectra of ClCN+ and BrCN+. These features and the vibrational frequency data are discussed.
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 117 (2002), S. 2003-2016 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present an ab initio theoretical study of five low-energy isomers of the water hexamer {Chair, Cage(du)[1], Book, Prism, and Boat}, their intramolecular vibrations, binding energies De and dissociation energies D0. Møller–Plesset second order perturbation calculations using the aug-cc-pVTZ basis set at aug-cc-pVDZ optimized geometries including vibrational zero point energy corrections predict Chair to be the most stable isomer, followed closely by Cage(du)[1] (+0.02 kcal/mol) and Book (+0.05 kcal/mol), while Prism is 0.15 kcal/mol higher. The Boat conformer is least stable at both the De and D0 levels. The main focus is on the intramolecular normal modes of the five isomers. The calculated O–H stretching frequencies and intensities are compared to recent infrared spectra of water hexamer in supersonic jets, liquid-helium droplets and solid para-hydrogen matrices. The IR spectra indicate that Book and Chair are major species in the latter two environments and may also exist in supersonic jets. The (H2O)6 gas phase interconversion equilibria are calculated and predict that the most abundant isomer is Chair below 8 K, Cage between 8–26 K, and Book above 26 K. Several of the low-frequency vibrational modes are identified as low-amplitude precursors of the Chair↔Book↔Cage isomerization pathways. © 2002 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 116 (2002), S. 1850-1857 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Accurate O–H(centered ellipsis)O hydrogen-bond dissociation energies were measured for the supersonic-jet-cooled complexes 1-naphthol⋅S with S=D2O, ethanol, oxirane, and oxetane. A mass-selective pump–dump–probe method was used, combining stimulated emission pumping with resonant two-photon ionization and ion-dip techniques. The ground-state dissociation energies D0(S0) are 5.83±0.13 kcal/mol for d1-1-naphthol⋅D2O, 7.94±0.02 kcal/mol for 1-naphthol⋅ethanol, 7.71±0.14 kcal/mol for 1-naphthol⋅oxirane and >8.17 kcal/mol for 1-naphthol⋅oxetane. The D0's increase by 5%–7% upon excitation of 1-naphthol to the S1 state. These dissociation energies are compared to those of the analogous complexes with S=H2O, methanol, NH3, and ND3 [Chem. Phys. Lett. 246, 291 (1996)]. The trends in D0 are compared to the electric dipole moments μ, molecular polarizabilities α¯, and gas-phase proton affinities of the H bond acceptor molecules. For the O-containing acceptors, the D0's correlate well with α¯, but the only good overall correlation for both O- and N-containing acceptors was found between the dissociation energies and proton affinities. © 2002 American Institute of Physics.
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  • 7
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 116 (2002), S. 2836-2847 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The S1↔S0 and S2↔S0 vibronic spectra of the supersonically cooled 2-pyridone dimer (2PY)2 and its 13C-, d1-, and d2-isotopomers were investigated by two-color resonant two-photon ionization and fluorescence spectroscopies. For the C2h symmetric (2PY)2–h2 and (2PY)2–d2 complexes, the 2PY moieties are equivalent and the S1↔S0 (1Ag↔1Ag) transition is forbidden. A single H/D or 12C/13C isotopic substitution reduces the symmetry to Cs, so that (2PY)2–13C and (2PY)2–d1 both exhibit S1↔S0 and S2↔S0 transitions. The S1/S2 state exciton splittings are 43.6 cm−1 and 52.4 cm−1, respectively. These are analyzed in terms of a Frenkel model and compared to calculated splittings based on ab initio monomer transition dipole moments. For (2PY)2–d1, whose 2PY subunits are different, an excitation transfer time of 318 fs is calculated from the exciton splitting. The S1↔S0 and S2↔S0 spectra are analyzed and assigned. Several bu intermolecular vibrations of S1 appear via vibronic coupling to the S2(Bu) state. Combination of the fluorescence data from excitation of the S1 and S2 origins and vibrational excitations of (2PY)2–h2, (2PY)2–d1, and (2PY)2–d2 allows the determination of the six S0 state intermolecular vibrational frequencies.© 2002 American Institute of Physics.
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  • 8
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The 2-pyridone⋅2-hydroxypyridine mixed dimer, 2PY⋅2HP, is linked by antiparallel N–H(centered ellipsis)N and O–H(centered ellipsis)O hydrogen bonds, closely analogous to tautomeric hydrogen-bonded DNA base pairs such as isoguanine⋅uracil. Mass-selected S1←S0 vibronic spectra of supersonic jet-cooled 2PY⋅2HP and three N–D or O–D deuterated isotopomers were measured by two-color resonant two-photon ionization and UV/UV-holeburning techniques. S1→S0 fluorescence spectra show intense hydrogen bond stretching vibrations ν6″=158 cm−1, observed for all four isotopomers and the weak ν5″ "shear" vibration at 116 cm−1. The "slanting" intermolecular vibration ν4″=89 cm−1 was tentatively identified via the 2ν4″ overtone. The observation of 2-pyridone intramolecular overtone and combination transitions for two out-of-plane modes indicate slight nonplanarity of the 2-pyridone moiety in the S1 state. Ab initio calculations using Hartree–Fock, configuration interaction among single excitations (CIS), and B3LYP density functional methods were employed to calculate ground- and excited-state structures, rotational constants, harmonic intermolecular and intramolecular vibrational frequencies, binding energies De, and dissociation energies D0. The B3LYP/6-311++(d,p) ν4″ and ν6″ frequencies are in very good agreement with the experimental ground-state intermolecular frequencies. Electronic excitation of the 2-pyridone moiety in 2PY⋅2HP leads to a decrease of dissociation energy by 2.36 kcal/mol and a concurrent increase of H bond lengths by (approximate)0.08 Å, in qualitative agreement with the self-consistent field (SCF) and CIS ab initio calculations. © 2001 American Institute of Physics.
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  • 9
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The structures and energetics of 23 different 7-hydroxyquinoline⋅(NH3)n clusters with n=1–6 are investigated using ab initio calculations at the SCF/6-31G** level. Clusters based on both the enol and keto tautomers of 7-hydroxyquinoline (7-HQ) are investigated, as well as ion-pair (zwitterionic) clusters resulting from proton transfer from 7-HQ to the (NH3)n cluster. In all cases, the solvent cluster forms hydrogen bonds at both the -O-H and N positions of 7-HQ. For n=2–4, ammonia-chain clusters are found, for n≥4, additional hydrogen-bond topologies appear such as bifurcated chains, cycles and mixed chain/cycles. Although the bare keto 7-HQ is calculated to be 17 kcal/mol less stable than the enol form, the energy difference decreases continuously to 11 kcal/mol for 7-HQ⋅(NH3)6 with increasing n. For one of the enol clusters involving six NH3 molecules, proton transfer can occur from either the -O-H or N-H group to the cluster, yielding a locally stable zwitterion cluster 7-HQ−⋅(NH3)6H+. For the keto tautomer, locally stable ion-pair clusters were found for n=2, 5, and 6, but these are calculated to be considerably less stable than the neutral enol forms. © 2001 American Institute of Physics.
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  • 10
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 560-565 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Mass- and isomer-selected S1←S0 resonant two-photon ionization and S1→S0 fluorescence spectra were obtained for the supersonically cooled 7-hydroxyquinoline⋅(NH3)n clusters with n=2–16. For n=2 and 3, the absorption and emission spectra exhibit discrete and narrow bands, characteristic of nonreactive hydrogen bonded ammonia-chain clusters. For n≥4, the S1←S0 R2PI spectra are completely broadened, with an onset at (approximate)355 nm. For n=4–7, a weak fluorescence emission is observed, Stokes-shifted by (approximate)185 nm, with a maximum at (approximate)540 nm, which shows discrete structure on a broad background. From comparison to fluorescence emission observed in bulk solution, we conclude that S1 state enol→keto tautomerization occurs. For the n≥7 or 8 clusters, the fluorescence emission spectra become completely unstructured and shift to the blue, peaking at 435–450 nm. This emission indicates the occurrence of either S1-state proton transfer to the ammonia solvent cluster and formation of the 7-HQ anion, or of the ground-state intracluster enol→keto tautomerization reaction. © 2000 American Institute of Physics.
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