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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 5154-5159 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Using a purely ab initio minimum energy path for the trans-tunneling motion in the HF dimer, the energy levels for the K-type rotation and trans-tunneling motion for (HF)2 and (DF)2 are calculated with a one-dimensional semirigid bender Hamiltonian and no adjustable parameters. The transition moments for rotation-tunneling transitions are calculated, using our ab initio value for the dipole moment of an isolated HF molecule, and we also calculate B¯ values. The energy levels we obtain are in close agreement with experiment; for example, the K=0 tunneling splitting in (HF)2 is calculated as 0.65 cm−1 compared to the experimental value of 0.658 69 cm−1. As well as showing that our ab initio minimum energy path is very good, the calculation demonstrates that the semirigid bender formalism is able to account quantitatively for the unusual K dependence of the rotational energies resulting from the quasilinear behavior, and that the trans-tunneling motion is separable from the other degrees of freedom. We use the results to predict the locations, and transition moments, of the ΔK=0 and ±1 subbands in the tunneling spectra of (HF)2 and (DF)2, many of which have not yet been observed.
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 6049-6054 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The infrared absorption spectrum of the acetylene–carbon monoxide van der Waals molecule has been obtained in the 3 μ region. A color center laser was used to excite the vibration of the complex which corresponds to the antisymmetric hydrogen stretching mode in the monomer in a pulsed molecular jet. The form of the spectrum indicates that the molecule is a linear, hydrogen bonded complex, although excited state perturbations are present. The vibrational origin is at 3279.898(2) cm−1 and the ground state B value is 1397.4(6) MHz, corresponding to a separation of 5.011 A(ring) for the monomer centers of mass. The spectrum cannot directly distinguish between the HCCH–CO and the HCCH–OC configurations, but the combined evidence of other hydrogen bonded complexes of carbon monoxide, the expectation that the observed hydrogen bond should be slightly shorter than the sum of van der Waals radii, and a distributed multipole analysis strongly favors the HCCH–CO configuration.
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 700-712 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The a-type, K=0 microwave spectrum of the N2–H2O complex has been observed using a pulsed molecular beam Fabry–Perot cavity microwave spectrometer. Seven isotopic species have been studied in the range of 5–23 GHz.The N2–H2O complex exhibits tunneling motions similar to the 1→2 tunneling motion of the H2O–DOD complex which gives rise to four components for each rotational transition. The molecular constants obtained for the ground tunneling (A1) state of 14N2–HOH are: B¯=2906.9252(2) MHz, DJ =0.043 486(15) MHz, and eQq(14N)=−4.253(2) MHz. The structure has a nearly linear N–N–HO geometry with a N–H distance of 2.42(4) A(ring) and an OHN angle of 169° [RO–N=3.37(4) A(ring)]. The electric dipole moment along the a principal axis of inertia was determined for the 15N2–HOH species with μa =0.833(3) D.
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  • 4
    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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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 4924-4933 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Far infrared laser–Stark spectroscopy is used to populate an excited vibrational state in the van der Waals molecule, ArHCl, in a molecular beam. Microwave–far infrared double resonance allows the identification of this state as the first excited bending state of Π symmetry. Subsequent radio frequency electric resonance of the vibrationally excited molecule combined with far infrared–radio frequency two photon experiments gives the following spectroscopic constants: ν0−B'=33.9248(7) (cm−1), B'=1695.(20) (MHz), μ=0.265(3) (D), eqQaa=12.(7) (MHz), eqQbb−eqQcc=−73.927(23) (MHz), q1=−49.583(2) (MHz). These constants are compared with theoretical predictions obtained using previously suggested potential energy surfaces and are related to the presence of other nearby vibrational states.
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 7001-7012 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A theoretical framework has been developed to describe the bending levels associated with an intermolecular potential of moderate anisotropy between an open-shell diatom and a diatom partner, such as OH–CO or OH–N2. The model explicitly allows for coupling between the electronic and spin angular momenta of the open-shell OH radical and the vibrational angular momentum arising from intermolecular bending motion of the complex. The energies and wave functions of the intermolecular bending levels for the OH–N2 complex have been computed based on a dipole–quadrupole interaction. The model is used to interpret the infrared spectrum of the linear OH–N2 complex in the OH overtone region, which has been recorded by detecting the OH fragments from vibrational predissociation. The pure OH overtone band at 6973.54(2) cm−1 and several combination bands, which involve the simultaneous excitation of OH stretching and geared bending modes, have been observed, analyzed, and assigned within the context of the model. In addition, the time evolution and quantum state distribution of the OH fragments yield the lifetime for vibrationally activated OH–N2 of 30±4 ns and an upper limit for the ground state binding energy of OH–N2, D0≤277 cm−1. © 2001 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. 913-923 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The infrared spectrum of the linear OD–N2 complex has been recorded in the OD overtone region near 1.9 μm using an infrared-ultraviolet double resonance technique. The pure overtone band of OD–N2(2νOD) was observed at 5173.99(1) cm−1, and combination bands involving the simultaneous excitation of OD stretch and geared bend were identified at 5209.02(1) cm−1 and 5214.59(2) cm−1. Assignments and spectroscopic constants have been derived from the rotationally resolved structure of each band, which are in good accord with model calculations based on an electrostatic interaction potential. Direct time–domain measurements yielded a vibrational predissociation lifetime of 150±16 ns for OD–N2 (2νOD) and a three fold decrease in lifetime upon intermolecular excitation of the lower-energy geared bending state. The OD (v=1) fragments of vibrational predissociation were found to be highly rotationally excited, indicating that predissociation proceeds by vibrational to rotational/translational energy transfer. The results obtained for OD–N2 are compared with an analogous study of OH–N2 [Marshall et al., J. Chem. Phys. 114, 7001 (2001)], revealing insights on the potential anisotropy along the geared bending coordinate and a change in the vibrational predissociation mechanism. © 2002 American Institute of Physics.
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  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 7298-7305 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The structure of the HBr OCS van der Waals complex has been studied by Fourier transform microwave spectroscopy. The ground state complex is hydrogen bound and quasilinear with SCO–HBr atomic ordering. Spectra from five different isotopomers were observed and assigned. The wide amplitude bending angle of the hydrogen bromide was calculated from the nuclear quadrupole coupling constant χaa to be 25.2°. Second order quadrupole effects, centrifugal distortion in the nuclear quadrupole coupling constant Dχ, a spin–rotation interaction, CBr, and a spin–spin interaction, Daa, were all included in the Hamiltonian. The following spectroscopic constants have been determined for the H79Br OCS isotopomer: B¯=488.7948(4) MHz; DJ=2.167(6) kHz; HJ=1.19(3) Hz; χaa=387.14(1) MHz; Dx=6.79(14) kHz; CBr=0.55(13) kHz; and Daa=7.7(1.2) kHz. © 1995 American Institute of Physics.
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  • 9
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 785-792 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Infrared optothermal laser spectroscopy has been used to study the linear SCO–HCN complex. The observed spectrum corresponds to excitation of the C–H stretching vibration out of either the ground state or v=1 of the lowest frequency intermolecular bending state. Ab initio calculations have also been carried out for this system which give, at least for some properties, results which are in good agreement with experiment. A comparison between the SCO–HCN results and those of the linear CO2–HCN complex studied previously, reveals that the shifts in the C–H vibrational frequency upon complex formation are rather similar. This is despite the fact that OCS and CO2 have very different point multipoles, suggesting that the electrostatic part of the interactions are likewise different for these two partners. Nevertheless, a distributed multipole calculation shows that, at the intermolecular separations characteristic of these complexes, the electrostatic interactions are in fact quite similar at the oxygen ends of OCS and CO2, providing an explanation for the similarity between the frequency shifts of these two complexes.
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  • 10
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 6334-6335 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The 3μ vibration–rotation spectrum of the HCCH–13CO van der Waals molecule is obtained and analyzed. Comparison with the results from an earlier study of the 12CO containing species provides experimental verification of the linear, carbon bonded structure proposed in the original work. Perturbations of the upper vibrational state in the 13CO isotopomer similar to those in the 12CO containing species are observed suggesting that a common state is responsible.
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