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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 18-24 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Spectra of the weakly bound van der Waals complexes H2–N2 and H2–CO have been studied in the mid- and far-infrared regions corresponding to H2 vibrational and pure rotational frequencies, respectively. The experiments were done using a Fourier transform infrared spectrometer to study equilibrium gas samples at low temperature (77 K) with a long absorption path. The spectra of the complexes appear as fine structure located near the peaks of the lines in the collision-induced spectrum of hydrogen. Compared to earlier studies of these species, the present results have more complete coverage of the various possible transitions, better resolution, and better signal to noise. New structure is reported which corresponds to hindered rotational transitions of the N2 component of an H2–N2 complex and is reminiscent of patterns observed for the N2–Ar and (N2)2 complexes. The relation of these results to far-infrared measurements of Saturn's satellite Titan, made by the Voyager spacecraft, is discussed.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 4039-4043 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The rotational analysis of the Coriolis-coupled ν2/ν3 bands in the infrared spectrum of the D2H+ molecular ion has been reexamined. By making four reassignments and adding one new transition, it has been possible to achieve a much better fit of the bands using fewer molecular parameters. The reassigned ν2/ν3 data were combined in a simultaneous least-squares analysis with existing ν1 band infrared data and with two newly measured pure rotational transitions. The resulting molecular parameters and calculated energy levels are the best currently available for this fundamental molecular ion.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 3261-3277 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Weakly bound complexes of molecular hydrogen have been studied using an infrared Fourier transform spectrometer and a long absorption path (112 m) through equilibrium gas mixtures at temperatures ∼20 K. Spectra of the dimers (H2)2, (HD)2, and (D2)2 were recorded, along with those of the mixed species H2–D2 and HD–D2. They lie in the 2900–8700 cm−1 (1.15–3.35 μm) spectral region corresponding to the monomer fundamental and first overtone bands. Since the rotation and vibration of the monomers remain largely unperturbed in a dimer, each dimer band is centered around a monomer rotation–vibration transition. The structure within these bands is associated with motions of the dimer as a whole, and particularly its end-over-end rotation, denoted by l. The spectra are quite detailed and well resolved, especially for the heavier isotopes HD–D2, and (D2)2, and in many cases, their rotational structure can be fully assigned. Although a detailed analysis is beyond the scope of the present paper, it should ultimately be possible to obtain precise multidimensional pair potential and induced dipole moment surfaces for molecular hydrogen directly from this experiment.
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 5313-5315 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The ν3 (O–Si stretch) fundamental bands of the HOSi+ and DOSi+ molecular ions in the 9 μm region have been detected for the first time, using a tunable infrared diode laser spectrometer and a hollow cathode discharge cell. Analysis of the results yielded accurate values for the molecular rotational and centrifugal distortion parameters, as well as for the band origins, which are 1127.009 cm−1 for HOSi+ and 1103.112 cm−1 for DOSi+ . The ground vibrational state parameters are in excellent agreement with those determined from the ν1 bands of the two isotopes.
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 2140-2147 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The spectrum of the linear carbon chain molecule C5 in the gas phase has been studied around 2170 cm−1, the region of the highest asymmetric stretching vibration ν3. The results were obtained using a tunable diode laser spectrometer and a cooled hollow cathode discharge in a flowing mixture of acetylene and helium. Four vibration–rotation bands were assigned and analyzed: the fundamental, a hot band arising from the v7=1, l=1 vibrational level, a second hot band arising from v7=2, l=0, and a third hot band tentatively ascribed to v5=1, l5=1. Small local perturbations were found to affect the upper vibrational states of two of the bands. Analysis of the data yielded accurate values for a number of molecular parameters for C5, e.g., the band origin ν3= 2169.4410(2) cm−1, the rotational constant, B0 =2557.63(9) MHz, and the l-type doubling parameters, q7=3.99(6) MHz, and q5=2.36(9) MHz. The value of q7 may be used to estimate a value of 118 cm−1 for the lowest bending frequency of the molecule. There is no evidence in C5 for quasilinear behavior such as that shown by C3 and C3O2.
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 3716-3723 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The ν2 (bending) fundamental band of CH2 in its X˜ 3B1 ground electronic state has been studied using tunable diode laser spectroscopy and also the LMR (laser magnetic resonance) technique in the 800–911 cm−1 and 1030–1173 cm−1 regions. For the diode laser study, a multiple-traversal absorption cell was used with Zeeman modulation, and the CH2 radicals were produced by a mild discharge in a flowing mixture of ketene (∼0.3 Torr) and helium (∼2 Torr). Under these conditions, the apparent lifetime of CH2 following cutoff of the discharge was about 1 ms. A total of 53 new transitions with rotational quantum numbers up to N=10, K‘a =3, and Ka =2 were observed to add to the 11 transitions previously measured in this band. A combined analysis of the present data and all the previous pure rotational and ν2 band results on CH2 has yielded an improved set of molecular parameters, including the first determination of centrifugal distortion effects for the dominant spin–spin interaction parameter, D. The present data have also been used in a comprehensive new analysis of triplet methylene rotation–vibration energies using the nonrigid bender Hamiltonian by Bunker et al. in an accompanying paper.
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  • 7
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 664-670 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The high-resolution absorption spectrum of the D2H+ molecular ion in the 1800–2300 cm−1 region has been measured in a discharge through a mixture of H2 and D2 using a tunable infrared diode laser source and a cooled hollow-cathode absorption cell. A total of 72 new lines of D2H+ have been observed, as well as five previously measured in ion-beam experiments by Wing and Shy, and these have been assigned to specific rotational transitions of the ν2 and ν3 fundamental bands. Two different and complementary theoretical models are used to fit these data: one is an A-reduced asymmetric rotor effective Hamiltonian including the Coriolis and higher-order rotational interactions between ν2 and ν3; and the other is a supermatrix model in which the matrix of the untransformed Hamiltonian is set up and diagonalized directly, using a large vibration–rotation basis that diagonalizes the vibrational energy. The former approach is less expensive and provides a better fit, but because of the large number of parameters varied may be more tolerant of incorrect assignments, whereas the latter is more expensive but may be more reliable because a smaller number of parameters is varied, most of the vibrationally off-diagonal parameters being constrained at values from ab initio calculations. These analyses have made it possible to assign 11 other lines observed by Wing and Shy, giving a total of 88 assignments. The observed band origins, ν2=1968.17 cm−1 and ν3=2078.42 cm−1, and rotational constants are in good agreement with recent ab initio calculations.
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  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 1146-1148 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The ν1 (C–D stretch) fundamental band of the DCO+ molecular ion has been studied using a tunable diode laser spectrometer and a liquid-nitrogen-cooled hollow-cathode absorption cell with magnetic field modulation. A total of eight lines were measured, and their analysis yielded the ν1 band origin, 2584.5618(14) cm−1, and the change in rotational constant, α1=226.3(11) MHz. The relatively small value of α1 as compared to theory and to the isoelectronic molecules DN+2 and DCN suggests the possibility of mixing between the (v1v2l2v3)=(1000) and (0400) vibrational states. The observation of ν1 for DCO+ means that 11 of the 12 fundamental bands have been observed for the isoelectronic family of molecular ions HCO+, DCO+, HN+2, and DN+2, leaving only ν2 of DCO+ still undetected.
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  • 9
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The observation of the high-resolution absorption spectrum of the H2D+ molecular ion in the region 2010–2610 cm−1 in discharges through mixtures of H2 and D2 gases is reported. Two types of tunable monochromatic sources are employed, either a diode laser (in Ottawa) or a difference-frequency laser system (in Chicago), and the sensitivity is improved by using either discharge modulation or Doppler velocity modulation techniques. A total of 66 new lines of H2D+ have been measured and assigned, mostly on the basis of ground-state combination differences, to specific rotational transitions of the ν2 and ν3 bands. These data, as well as the two known microwave lines, are fitted by means of two theoretical models, either an effective Hamiltonian model including a Padé representation of a conventional A-reduced centrifugal Hamiltonian for each vibrational level together with Coriolis and higher rotational interactions between ν2 and ν3, or a supermatrix model in which the matrix of the untransformed Hamiltonian is set up in a large vibration-rotation basis and diagonalized directly. In the supermatrix model most of the vibrationally off-diagonal matrix elements are constrained to values derived from Carney's ab initio calculations, while the ν1 parameters are fitted to the observed lines of Amano. Because of the large number of parameters required in the effective Hamiltonian, the less flexible supermatrix model was valuable as a check of the assignments. The results of these fits make it possible to assign seven of the nine lines reported by Shy, Farley, and Wing in 1981. The observed band origins, ν2=2205.87 cm−1 and ν3=2335.45 cm−1, as well as the rotational constants, are in good agreement with ab initio predictions. With the use of one calculated term value to relate the stacks of levels with even and odd values of K‘a, a table of observed term values of the lower rotational levels of the ground state and the ν2 and ν3 states is constructed.
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  • 10
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 117 (2002), S. 2586-2591 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Infrared spectra of the weakly bound complexes N2O–4He, N2O–3He, and OCS–3He have been observed using a tunable diode laser to probe a pulsed supersonic jet expansion. The rotational structure of the bands was analyzed using a conventional asymmetric rotor Hamiltonian. The N2O–3He and OCS–3He spectra are mostly a type (ΔKa=0) in structure, with very weak b-type (ΔKa=±1) transitions, but for N2O–4He the a- and b-type components are both prominent. The fitted rotational parameters are consistent with roughly T-shaped structures with intermolecular separations around 3.4–3.5 Å for N2O–He and 3.8–3.9 Å for OCS–He. The angle between the N2O or OCS axis and the He position is about 80° for N2O–He and 65° for OCS–He. The vibrational band origins are slightly blueshifted from those of the free molecule, with the N2O–He shifts (+0.2 cm−1) being about twice the magnitude of the OCS–He shifts (+0.1 cm−1). The results are of particular interest since N2O and (especially) OCS have both been used as probes in experiments on ultracold helium nanodroplets. © 2002 American Institute of Physics.
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