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  • 1985-1989  (17)
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  • 1
    Digitale Medien
    Digitale Medien
    The anisotropic potentials of He–N2, Ne–N2, and Ar–N2 (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 5465-5474 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The anisotropic potentials of He–N2, Ne–N2, and Ar–N2 are predicted using the Tang–Toennies potential model. This model damps the long-range ab initio dispersion terms individually using a universal damping function and adds to this a simple Born–Mayer repulsive term. The Born–Mayer parameters for the three systems were derived from SCF calculations. The dispersion coefficients were estimated from established combining rules using an effective multipole spectrum for the N2 molecule computed by Visser and Wormer from the time-dependent coupled Hartree–Fock approximation. The resulting potentials were used to predict the second interaction virial coefficients for each system, and they are found to be in excellent agreement with experiment. It is concluded that the spherical symmetric potentials are within 2%–3% of the true potentials. Some discrepancies with recent molecular beam experiments appear to be present, however, for the anisotropies especially in the case of He–N2. Finally, it is found that the law of corresponding states for anisotropic systems, which predicts that the reduced shapes of the potentials for a given geometrical configuration are identical, also holds for the highly anisotropic rare gas–N2 systems.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.454557
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  • 2
    Digitale Medien
    Digitale Medien
    Erratum: Scattering of highly vibrationally excited Li2 from He and Kr [J. Chem. Phys. 85, 7062 (1986)] (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 5986-5986 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.454771
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  • 3
    Digitale Medien
    Digitale Medien
    A three-dimensional quantum mechanical study of vibrationally resolved charge transfer processes in H++H2 at Ecm=20 eV (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 4169-4182 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: A three-dimensional quantum mechanical study of vibrational state resolved differential cross sections for the direct inelastic and charge transfer channels of the H++H2 system has been carried out at Ecm =20 eV using the infinite order sudden approximation (IOSA). Steric factors, opacity functions, angular distributions, and integral cross sections are calculated. The integral cross sections are in very good agreement with recent experimental results, whereas the angular distributions agree only partially with the experiments. A further comparison of both the theoretical and experimental results with semi-classical calculations based on the usual trajectory surface hopping method revealed that the present quantum results provide a better description of the experimental observations. The likely shortcomings of the semiclassical method are discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.456794
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  • 4
    Digitale Medien
    Digitale Medien
    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
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: 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)
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.454217
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  • 5
    Digitale Medien
    Digitale Medien
    Vibronic energy distribution of H2O+ produced in charge transfer scattering of D+ by H2O (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 1447-1448 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: A crossed beam study of the charge exchange reaction between deuterons and water molecules is reported. Individual vibronic states of the triatomic molecular ion produced in collisions are resolved.(AIP) e
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.453277
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  • 6
    Digitale Medien
    Digitale Medien
    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
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.454380
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  • 7
    Digitale Medien
    Digitale Medien
    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
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: 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%).
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.454467
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  • 8
    Digitale Medien
    Digitale Medien
    Scattering of highly vibrationally excited Li2 from He and Kr (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 7062-7076 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Total integral scattering cross sections have been measured for Li2 molecules in selected rotational and vibrational states up to v=21. The vibrationally highly excited states with energies up to 80% of the dissociation energy were prepared by Franck–Condon laser pumping. With increasing vibrational quantum number the observed cross sections show first a 10% decrease followed by a 20%–25% rise. A model potential has been developed based on an ab initio potential for the vibrational ground state to account for the effect of vibrational stretching. The results provide for the first time direct information on the bond-distance dependence r of the complete potential hypersurface V(R,r,γ) (R distance between centers of mass and γ angle between r and R) of an atom–molecule system.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.451393
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  • 9
    Digitale Medien
    Digitale Medien
    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
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.451632
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  • 10
    Digitale Medien
    Digitale Medien
    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
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.449319
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