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  • 1985-1989  (17)
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  • 1
    Electronic Resource
    Electronic Resource
    A comparison between theoretical and experimental state-to-state charge transfer cross sections for H++H2 at 20 eV: Evidence for quantum effects (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 1461-1463 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A three−dimensional close coupling quantum mechanics calculation is performed for hydrogen ion−molecule collisions. The results are compared to those obtained from the trajectory surface hopping method. (AIP)
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454217
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Interaction potentials for alkali ion–rare gas and halogen ion–rare gas systems (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 6290-6302 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The Tang–Toennies model [J. Chem. Phys. 80, 3725 (1984)] has been modified to predict the potentials for ion–atom systems. First order SCF energies are used to describe the repulsive potential. The long range second order induction and dispersion potential terms up to R−10 are either taken from ab initio calculations or estimated and each term is appropriately damped. The potentials for Li+, Na+, K+, F−, and Cl− interacting with He, Ne, and Ar are found to agree well with both theoretical and experimental data within the expected errors. For comparison with the model new ab initio calculations have been performed for Na+–Ar and the results are in excellent agreement with the model predictions (〈10%).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454467
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Vibrationally resolved inelastic and charge transfer scattering of H+ by H2O (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 5256-5265 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Inelastic and charge transfer scattering of protons by water molecules at collision energies of 27.0 and 46.0 eV have been investigated in a high-resolution crossed beam experiment up to the rainbow scattering angles. Excitation of the stretching (symmetric or asymmetric) and bending mode vibrations within the electronic ground state, X 1A1, of H2O was observed in the proton energy-loss spectra. In the case of charge transfer, formation of H2O+ in the X˜ 2B1 and A˜ 2A1 electronic states was identified in the corresponding H-atom spectra; the vibrational states within the X˜ and A˜ bands were for the most part resolved and, at small angles (θ≤2°), they were found to be nearly the same as in photoionization (symmetric stretch and bending mode excitation within the X˜ state and pure bending mode excitation within the A˜ state). The vibronic transition probabilities deviate, however, considerably from the corresponding Franck–Condon factors in favor of the enhancement of the quasiresonant states. For both the inelastic and charge transfer scattering, state-selected quantities characteristic of the detailed collision dynamics have been derived. In addition, rotational excitation superimposed on the vibrational transitions could be estimated and for both processes it was found to be of the order of 50–100 meV.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453668
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Charge transfer and structured vibrational distributions in H++CH4 low-energy collisions (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 6814-6830 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Inelastic and charge transfer collisions of protons with methane molecules have been investigated in a perpendicular-plane crossed beam experiment via the detection of the scattered protons and H atoms, respectively. Time-of-flight analysis of the protons and H atoms at scattering angles 0°≤θ≤10° and collision energies 10≤E≤30 eV provided information on internal energy distributions of the CH4 and CH+4 products. Excitation of the n(ν1 ,ν3) +m (ν2 ,ν4) type vibrations, with n,m=0, 1, 2,⋅⋅⋅was found to be the most probable assignment of the observed structured energy distributions of CH4 (1 A1 ) at θ≤4°. At θ〉4°, the energy transfer increases steeply up to the dissociation limit while the vibrational structure was no longer resolved. In the case of charge transfer, the observed narrow internal energy distributions corresponding to a most probable average internal energy of CH+4 of about 0.95 eV was centered at the recombination energy of the proton indicative of quasiresonant charge transfer. In addition, fragmentation of CH+4 formed in charge transfer collisions of H+ with CH4 was investigated in an independent experiment using mass spectrometric analysis to identify the individual fragment species. The relative intensities of the parent and fragment ions (i.e., of CH+4, CH+3, and CH+2) were found to be in good agreement with the known values of the appearance potentials of the fragment ions and the distribution of the CH+4 internal energy as obtained from the differential cross sections. A mechanism is proposed to explain the experimental results based on vibronic symmetry correlation theory. This mechanism deals with vibronic interactions in the compound quasimolecule CH+5 and explains the origin of the unexpected excitation of infrared inactive modes [e.g., ν2 (E)] of the tetrahedral methane. The effects of Jahn-Teller distortions of the CH+4 charge transfer product are also discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454380
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  • 5
    Electronic Resource
    Electronic Resource
    Vibrational state resolved measurements of differential cross sections for H++O2 charge transfer collisions (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 3313-3325 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Vibrational state-to-state charge transfer cross sections have been obtained for H++O2 collisions at Ecm =23.0 eV in a differential scattering experiment by measuring the product H atom energy distribution in the range 0°≤θ≤11°. The results show a strong dependence of the distribution of vibrational transition probabilities P(O2, v=0→O+2, v″) on the scattering angle. At very low angles (θ(approximately-less-than)2°) we find a strongly enhanced contribution of the more resonant states v″=3–6 compared to a Franck–Condon distribution, which is peaked at v″=1 and, on the other hand, at moderate angles of about θ=4° comes very close to the measured spectra. At even larger angles increasing deviations from the Franck–Condon distribution towards larger excitation of higher vibrational states are observed. An explanation of these and the related results for the nonexchange collisions leading to neutral O2 vibrational excitation is given in terms of the underlying potential energy surfaces.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.450952
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  • 6
    Electronic Resource
    Electronic Resource
    Molecular beam scattering measurements of differential cross sections for D+H2(v=0)→HD+H at Ec.m.=1.5 eV (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 6396-6419 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The reaction D+H2→HD+H has been studied in a crossed molecular beam scattering experiment at a most probable collision energy of Ec.m.=1.5 eV. Angular and time-of-flight distributions of the HD product have been measured over a wide range of angles. The experimental data are compared with quasiclassical trajectory (QCT) calculations on the LSTH potential hypersurface. The QCT calculations fit the experimental data quite satisfactorily. The sensitivity of the experiment to the different properties of the cross section has been investigated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451470
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    Paper (German National Licenses)
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  • 7
    Electronic Resource
    Electronic Resource
    Time-of-flight spectroscopy of high-overtone mode-selective vibrational excitation of CF4 and SF6 in collisions with H+(D+) at energies between 10 and 28 eV (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 2259-2279 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Time-of-flight spectra for H+(D+)–CF4 and SF6 collisions have been measured with an improved resolution and at higher collision energies (10≤Elab ≤28 eV) compared to earlier work. In the low energy region (≤13 eV) new distinct peaks are resolved for both molecules corresponding to small contributions from the second infrared active ν4 mode in addition to the dominant ν3 mode observed previously. Reexamination of experimental vibrational transition probabilities reveals an almost perfect agreement with a Poisson distribution for both modes up to the n=6 overtone transition of ν3. A simple straight line theory is used to calculate the energy transfer in small angle scattering from the long-range potential in good agreement with a full classical trajectory calculation. With this theory dipole moment derivatives can be determined directly from the observed energy transfers and are found to agree well with previous infrared measurements. At larger collision energies (≥16 eV) an additional low intensity vibrational distribution is identified in the high energy loss tail of the spectra which can be attributed to small impact parameter collisions which probe the repulsive region of the potential. The observed energy transfers are also in good agreement with trajectory calculations indicating that the forced oscillator model is also applicable in the repulsive potential region for the present systems. A closer examination of the high energy loss tail reveals resolved structure which has been assigned to discrete states of the ν3 mode in CF4 up to the n=14 overtone. These new results demonstrate that H+(D+) energy loss scattering can provide spectroscopic information not readily available from other experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.449319
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    Paper (German National Licenses)
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  • 8
    Electronic Resource
    Electronic Resource
    Quantum calculations for diffractive and rotationally inelastic H2/LiF (001) scattering (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 827-834 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Exact close-coupling calculations for H2 rigid rotor scattering from a LiF (001) surface are presented. Using a standard model potential, rotation-diffraction transition probabilities are reported for a range of collision energies up to 0.7 eV and for various surface corrugations. The calculations are aimed to serve as a reference for approximate approaches. The exact transition probabilities are compared with existing quasiclassical trajectory calculations and with results obtained by the matrix-diagonalization sudden method. In agreement with previous approximate treatments it is found that the coupling between rotations and diffractions is only weak so that both can essentially be treated independently.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.449497
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  • 9
    Electronic Resource
    Electronic Resource
    Predominance of CF-stretch vibrational excitation in state resolved inelastic scattering of protons from 11 small fluorohydrocarbon molecules (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 217-225 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Time-of-flight spectra of H+ scattered from all ten different fluorinated hydrocarbon molecules of type CHmFn and C2HmFn (m+n=4) as well as C2F6 have been measured for small scattering angles (θlab≤15°) at 9.8 eV collision energy. For the pure hydrocarbons the spectra show a complicated structure suggesting unresolved excitation of several modes and a significant effect of charge transfer collisions. In contrast all the spectra for fluorine containing molecules exhibit more or less sharp maxima indicating high overtone excitation of predominantly one vibrational mode with ω(approximately-equal-to)1200 cm−1 corresponding to a CF-stretch vibration. At some scattering angles the overtone transition probabilities deviate somewhat from a Poisson distribution suggesting small unresolved contributions from additional vibrational modes. Over- all, however, there is good agreement for the low symmetry molecules, some of which have sizable dipole moments, with the predictions of the simple forced oscillator model previously tested only for the spherically symmetric molecules CF4 and SF6. The relative magnitudes of the observed energy transfers are consistent with absolute infrared intensities where these are available from the literature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.448793
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  • 10
    Electronic Resource
    Electronic Resource
    Theory of resonant inelastic one-phonon scattering of He atoms from a LiF(001) single crystal surface (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 532-552 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: For the He–LiF(001) system, molecular beam measurements of the inelastically scattered intensity have revealed a large number of resonance structures. In this paper the theoretical description of these resonant inelastic one-phonon scattering processes is provided in the framework of the distorted wave Born approximation. In the first step the elastic diffractive scattering problem is solved exactly using close coupling calculations for a recently developed pairwise additive semi ab initio potential and a rigid lattice. As the potential contains both the attractive well and the corrugation in a realistic manner, bound state resonances are fully taken into account. In the next step the inelastic coupling due to one-phonon processes is treated as a perturbation of the elastic wave functions obtained from the close coupling solutions. The inelastic coupling potential is the same semi ab initio two-body potential used to describe the atom–static surface potential, and the LiF–surface lattice dynamics are described by realistic Green's function calculations. The theoretical results provide a good description of most of the structures seen in experimental angular distributions and time of flight spectra. The resonant features can be interpreted in terms of one-phonon assisted adsorption into and desorption out of specified bound states of the atom–surface potential. In addition to the contributions of Rayleigh phonons the bulk phonons contribute about 40% to both the creation and annihilation inelastic scattering processes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451632
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