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  • 1
    Electronic Resource
    Electronic Resource
    The vibrational line shape of diatomic adsorbates on metal clusters (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 862-870 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A decrease of at least an order of magnitude in the vibrational relaxation time T1 has been measured for CO bonded to Rh and Co clusters when the size of the cluster increases from 5 to 35 A(ring). We propose that this effect is mainly due to the coupling of the molecular vibration ω0 with the electron-hole excitations in the cluster. This is described via a model Hamiltonian. The finite size of the clusters give rise to a discrete electronic spectrum, and hence to a discrete pair excitation spectrum. This effect is measured in terms of D, the mean spacing between nearest-neighbor levels in the conduction band of the cluster. We find that: (1) the proposed mechanism starts to contribute to T1 only when D〈(h-dash-bar)ω0; (2) T1 is at least several hundred ps for clusters less than 15 A(ring) in size; (3) there is a sharp decrease of T1 to about 10 ps as the cluster size increases from 15 to 40 A(ring); (4) T1 decreases smoothly towards the bulk value for larger clusters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463189
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  • 2
    Electronic Resource
    Electronic Resource
    Resonance enhanced electron stimulated desorption (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 3174-3181 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A theory is presented which accounts for "giant'' enhancements in electron stimulated desorption (ESD) yields from adsorbate-covered surfaces if the incident electrons become trapped in a shape or Feshbach resonance associated with the adsorbate. The resulting temporary negative ion is displaced inwards towards the surface as a result of the force provided by the image screening charge. Upon reneutralization, the "desorbate'' can be returned high on the dissociative repulsive wall of the neutral-surface potential curve. This process has been modeled within the context of semiclassical Gaussian wave packet dynamics. Recent observations of such giant enhancements in the ESD yields for the system O(a)/Pd(111) are explained in terms of this model, and an atomic physics basis for the resonance in atomic oxygen is proposed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456938
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  • 3
    Electronic Resource
    Electronic Resource
    Electron-stimulated desorption and surface species conversion: The observation of a desorption resonance for atomic oxygen on the Pd(111) surface (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 5793-5800 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The influence of electron bombardment on an oxygen-covered Pd(111) surface at 87 and at 300 K has been studied by temperature programmed desorption. It is found that electron bombardment of an O2(a) adlayer at 87 K leads to the depletion of O2(a) and the conversion to O(a) with about the same cross sections, ∼1×10−17cm2 (Ve =200 eV). The O2(a)-depletion process is preferred at higher O2(a) coverage as the availability of open sites limits the O2(a) conversion. The new channel for conversion to O(a) due to electron bombardment results in a maximum increase of O(a) coverage by 88% and an additional desorption feature at 704 K compared to the usual temperature programmed desorption behavior due to O(a) recombination. The cross sections for desorption and conversion of O2(a) exhibit different electron energy dependence, suggesting that different primary electron excitations are involved in the two processes. The cross section for the electron-stimulated desorption of atomic oxygen is observed to be strongly dependent on electron energy, with its maximum value being ∼1.2×10−17 cm2 at an electron energy of 10±2 eV. The behavior of the cross section as a function of electron energy suggests the involvement of a surface resonance near 10 eV. A possible mechanism for resonance enhanced desorption is suggested, based on semiclassical wave packet propagation over potential energy curves which are consistent with the excitation spectrum of oxygen negative ions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456686
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  • 4
    Electronic Resource
    Electronic Resource
    NO electronic desorption processes from step sites on Pt(112): A comparison between photo- and electron-stimulated desorption (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 4373-4378 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Using Fourier-transform infrared reflectance absorption spectroscopy as a surface analytical method, the total photo- and electron-stimulated desorption cross sections for specific chemisorbed NO species on the steps of Pt(112) have been measured. These species-specific cross sections for photo- and electron stimulated desorption are compared with each other. An unexpected result was obtained for photo-stimulated desorption, using photons with an energy of 3.5 eV; bridged-NO desorbs with a higher cross section (1.1×10−22 cm2) than terminal-NO (6.1×10−23 cm2). For electron stimulated desorption, using electrons of an energy of 275 eV, the opposite is observed. Terminal-NO desorbs with a higher cross section (2.3×10−18 cm2) than bridged-NO, with a cross section of 8.7×10−19 cm2. The photo-stimulated process is discussed within the "hot electron'' model, and it is postulated that the higher expected quenching rate of the NO−(a) species produced from the more strongly-bound bridged-NO is more than compensated by propagation of the short-lived intermediate NO−(a) toward the metal surface. This leads to a closer approach to the surface of NO−(a) produced from bridged-NO than from terminal-NO, giving a higher probability of photodesorption of bridged-NO compared to terminal-NO. For the bridged-NO species, this is due to a steeper slope of the NO−(a) potential energy surface at the Franck–Condon excitation point compared to the slope for the terminal-NO which is initially located further from the surface. Electron stimulated desorption yields the expected relationship between the total desorption cross section for bridged- and terminal-NO, with the more strongly-bound bridged-NO having the smaller cross section. Here it is postulated that bridged- and terminal-NO connect to highly-excited NO states which do not differ so much in their dynamical interaction with the surface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467488
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  • 5
    Electronic Resource
    Electronic Resource
    Energy dependence of collision characteristics in molecule-surface collisions (1992)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 96 (1992), S. 7870-7873 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100199a008
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  • 6
    Electronic Resource
    Electronic Resource
    Vibrational excitation in molecule–surface collisions. Analytic modeling vs classical trajectories (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 5196-5210 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The problem of translational to vibrational energy redistribution occurring in collisions between diatomic molecules and solid surfaces is considered. Attention is focused solely on a mechanism which is a consequence of a molecule–surface interaction giving rise to an intramolecular potential whose equilibrium separation is a function of distance from the surface. This "three-body'' chemical effect is totally unrelated to mechanical excitation due to spring compression. While past work has emphasized the specific process of charge transfer/harpooning as a means for obtaining such an interaction, the mechanism is more general in the sense that it depends only upon the topology of the potential energy surface (PES) and not on what electronic properties gave rise to the topology. The T to V energy redistribution is treated both within the context of analytical models over necessarily simplified PES as well as numerically evaluated classical trajectories over more complex and realistic ones. Systematic studies are presented in which the relationship between energy conversion and PES characteristics are established. Conditions under which the analytic models provide reasonable representations of the collision are noted. I2 is the molecule of choice in this work.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452641
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  • 7
    Electronic Resource
    Electronic Resource
    The Semiclassical Way to Molecular Dynamics at Surfaces (1988)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Physical Chemistry 39 (1988), S. 395-424 
    Details
    ISSN: 0066-426X
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.pc.39.100188.002143
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  • 8
    Electronic Resource
    Electronic Resource
    Collision induced dissociation of diatomic molecules on surfaces: A charge transfer mechanism (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 3502-3508 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A theory is presented which accounts for one of the possible mechanisms responsible for dissociative scattering of diatomic molecules from surfaces. If on the incident trajectory of the molecule, a surface-to-molecule electron transfer occurs and on the outgoing trajectory, the reverse, then the temporary negative molecular ion formed for the time duration between electron hops will displace in its intramolecular vibrational coordinate. The molecule will emerge as a vibrationally excited neutral, with some of the excited states lying within the dissociative continuum. A model is described for this process in which the center-of-mass translational motion is handled classically and the intramolecular motion via wave packet dynamics. The theory is energy and probability conserving and microscopically reversible. Dissociation probabilities calculated as a function of incident energy and system parameters are discussed in the light of experimental measurements for the system of I2 dissociatively scattered from MgO surfaces.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.450236
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  • 9
    Electronic Resource
    Electronic Resource
    Charge transfer, vibrational excitation, and dissociative adsorption in molecule–surface collisions: Classical trajectory theory (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 5203-5215 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The consequences of charge transfer processes occurring when a molecular beam of diatomic molecules is directed upon a solid surface are here considered. In analogy with resonance electron scattering from molecules or harpooning processes in atom–diatom collisions, the incident beam could either be scattered into a highly vibrationally excited molecular state, dissociatively scattered, or dissociatively adsorbed due to formation of temporary negative molecular ions which enable redistribution of the incident translation energy of the beam into intramolecular degrees of freedom. In this work, the exact classical trajectories for the diatomic molecule, including internal vibrational motion, are calculated for motion over model diabatic potential surfaces in which surface hopping due to charge transfer/harpooning is accounted for. Connections between classes of trajectories and topological features of the potential energy surfaces (PES) are illustrated. The model is used to study the average translational to vibrational energy transfer as a function of incident kinetic energy and of PES parameters. Branching ratios between scattered and dissociatively adsorbed molecules are obtained as a function of both incident translational and total energy and the role of the intermediate negative ion resonance in influencing the dynamics of molecular processes at surfaces is illustrated. Comparison with quantum mechanical theories is given in a subsequent paper.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.448645
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  • 10
    Electronic Resource
    Electronic Resource
    Pumping and probing: Vibrational relaxation in time domain spectroscopy (1990)
    Springer
    Applied physics 51 (1990), S. 108-114 
    Details
    ISSN: 1432-0630
    Keywords: 68.35 J
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Various aspects of experiments on vibrational relaxation of molecules adsorbed on metals are considered. The necessity for time-domain pump-probe configurations is established. Since existing experiments to date have been carried out on small metal clusters, special attention here is given to the role of quantum size effects and the resulting role of the discrete electron-hole pair excitation spectrum on the observed energy/vibrational relaxation times.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00324272
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