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  • 1
    Electronic Resource
    Electronic Resource
    Extraction of kinetic parameters in temperature programmed desorption: A comparison of methods (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 6725-6732 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An investigation of the temperature programmed desorption (TPD) of CO and D2 from Ni(111) has been carried out. It has been shown that a differential method for the extraction of the kinetic parameters, threshold temperature programmed desorption (TTPD), can be applied with accuracy near the limit of zero coverage. In this limit, agreement is found between integral and differential methods for kinetic parameter evaluation. The factors which limit the applicability of TTPD are explored and a method to verify its proper application is presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453409
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  • 2
    Electronic Resource
    Electronic Resource
    Potential energy curves for the a 3Σu+ and c 3Σ+g states of He2 consistent with differential scattering, ab initio theory, and low-temperature exchange rates (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 6719-6727 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Crossed beam scattering experiments on He*(2 3S)+He at energies of 0.94, 1.51, and 2.24 kcal/mol have been combined with ab initio theory and kinetic data on metastability exchange rates to produce new estimates of the title potential energy curves. The long-range potential barrier in the a state is found to be 1.43±0.05 kcal/mol at a separation of 2.717±0.04 A. Combining these results with those for the corresponding singlet states from an earlier paper [J. Chem. Phys. 80, 5027 (1984)], we discuss the long-range behavior of the curves, particularly with respect to curve crossing between a given pair of g and u states. These crossings, which conform to theoretical predictions, appear to be essential for a consistent description of all available data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.450674
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Angle-energy distributions of Penning ions in crossed molecular beams. I. Evidence for discrete nonadiabaticity in the He*(2 1S)+H,D→He+H+,D++e− reaction (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 2588-2599 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Relative doubly differential cross sections for the Penning ionization of H and D by He*(2 1S) are reported at a mean collision energy of 9.2 kcal/mol for H and 7.9 for D in an experiment employing crossed supersonic beams and a rotatable mass spectrometer detector. The products are scattered sharply forward in the center-of-mass frame, with release of an additional 3.5 kcal/mol into translational energy at the peak of the recoil distribution. The energy release is significantly lower than predicted on the basis of quantum dynamics on a single adiabatic ab initio complex potential, or of the experimental low-energy Penning electron spectrum (PIES). Discrete nonadiabatic behavior is suggested and a model is developed based on modifications of ab initio potentials, Penning ionization atom–atom theory on a single complex potential, and an adiabatic-velocity modification of Landau–Zener curve-crossing theory (which may be more generally useful). The dynamical model compares well with exact two-state complex potential calculations for the magnitude and energy dependence of the total ionization cross section, and improves the emulation of both the low-energy PIES data and our recoil distributions. Significant modifications to the ab initio potentials include a deepening of the well in the He*(2 1S)+H adiabatic potential by 2.0 to 10.2±1 kcal/mol, a quadrupling of the magnitude of the resonance width, and a reduction in the adiabatic splitting at the avoided crossing between 2 1S and 2 3P potentials. Our low-energy calculations suggest that available data on the associative ionization (HeH+) branching fraction is inconsistent with the PIES data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459835
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  • 4
    Electronic Resource
    Electronic Resource
    A comparative kinetic study of xenon adsorption on a flat Pt(111) and stepped Pt(557) and Pt(112) surfaces (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 7690-7699 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The adsorption and desorption kinetics for Xe on three Pt single crystalline surfaces have been measured using threshold temperature programmed desorption measurements. It has been found that the first-order desorption kinetic parameters at zero coverage for Xe on Pt(111) (E0d =5.73±0.50 kcal/mol; ν0d=1012.5±0.9 s−1) are in excellent agreement with measurements made by a modulated molecular beam method [E0d =5.65±0.35 kcal/mol; ν0d=1012.1 s−1]. The presence of step defect sites of varying density on Pt(557) (1/6 defects) and on Pt(112) (1/3 defects) is shown to have a marked influence on Xe desorption kinetics, producing larger values of E0d(approximately-equal-to)8.5–8.7 kcal/mol and larger values of ν0d (approximately-equal-to)1014 s−1 compared to Pt(111). In addition, for Pt(111), slight attractive Xe–Xe interactions are observed, whereas for Xe adsorption on step sites, repulsive Xe–Xe interactions are observed as the steps fill. Xe adsorption kinetics on Pt(111) at 87 K are consistent with an island growth mechanism. In contrast, on Pt(557) and Pt(112), the adsorption process does not seem to produce island growth on the terraces. These results, taken together, show that using Xe, defect sites on metals may be probed effectively with adsorption and desorption kinetic methods.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458155
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Angle-energy distributions of Penning ions in crossed molecular beams. II. Effect of Penning electron recoil in Ne*(3s 3P2)+H,D→Ne+H+,D++e− (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 3371-3380 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Relative doubly differential cross sections for Penning ionization in the title systems are reported at a mean collision energy of 10.4 kcal/mol in a crossed supersonic beams experiment. As in paper I of this series on He*(21S)+H,D, the H+,D+ products are scattered sharply forward with respect to the incident H,D in the center-of-mass frame, but with the release of an additional 30 kcal/mol into translational energy at the peak of the distribution. Unlike the results of paper I, we find that a single optical potential, corresponding to an autoionizing state of NeH of assumed 2Σ+ symmetry, consistently represents the main features of both previously reported low-energy Penning ionization electron spectroscopy (PIES) data and the present results. Agreement between theory and experiment in the angular distributions is improved by including coupling between the angular momenta of the Penning electron and the atoms after ionization. The resonance width for PI is found to be nonexponential, showing a "saturation'' effect at small distance. This is interpreted in terms of the ionic (charge transfer) character of the bonding in NeH*.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460842
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    Paper (German National Licenses)
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