Dynamics of gas–surface energy transfer: Inelastic scattering of NO from Ag(111)

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Abstract
We have determined the velocity distributions of individual quantum states of NO scattering from Ag(111) using molecular-beam techniques to control the incidence energy Ei and angle θi, and detecting individual quantum states of NO at specific scattering angles θf and surface temperatures Ts by two-photon ionization. Here, Ei has been varied between 0.1 and 1.0 eV, θi from 15° to 65°, θf from 0° to 75°, and Ts from 155 to 760 K, with a total of over 1000 such velocity distributions. We report the observation of direct vibrational excitation and of an anticorrelation between translational energy loss to phonons and to rotation. We also show that this system is highly translationally inelastic with up to 55% of Ei being lost to phonons at Ei=1.0 eV and that the final translational energy is rather insensitive to θf. Angular distributions are found to depend on the degree of rotational excitation, but to a much lesser extent than would be expected for direct transfer of normal energy into rotation. Results are discussed in terms of an electronic mechanism for vibrational excitation, trajectory calculations, and simple models.

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