Inelastic scattering of NO from Ag(111): Internal state, angle, and velocity resolved measurements

Abstract

We have determined the velocity distributions of individual quantum states of NO scattering from Ag(111) at specific scattering angles θf using molecular beam techniques to control the incidence energy Ei and angle θi. We find that the mean energies of scattered species Ef depend weakly on θf at low collision energies, but become increasingly independent of this parameter as Ei approaches 1.0 eV. This is true for all final rotation states J. The previously reported insensitivity of the final kinetic energy to J is found to apply at all scattering angles, so that Ef vs θf curves for high J fall only slightly below those for low J. This system is highly translationally inelastic at high incidence energies, with up to 55% of Ei being lost to phonons at Ei=1.0 eV. Angular distributions are relatively insensitive to J at low Ei, but for high Ei the peak flux is found to shift away from the surface normal as Ei increases. The effect of the surface temperature only becomes apparent at low incidence energies. A search for supernumerary rotational rainbows reveals no discernible oscillations even for the lowest surface temperatures. We believe that these supernumerary oscillations may be damped by ‘‘surface corrugation’’ effects for this system. Discussion focuses on the observed anticorrelation between kinetic energy transfer to phonons and to rotation, the extent to which parallel momentum is conserved in this system, and energy-angle scaling laws for energy transfer. In this latter case we show that energy transfer in this system scales approximately with the quantity Ei cos θi, over the full range of conditions covered.