Energy and momentum distributions versus incident energy in the scattering of CO from Ag(111)

Abstract

The effect of changing the incident translational energy on the exit translational energy, rotational state population distributions, and angular momentum alignment of monoenergetic, rotationally cold CO scattered from Ag(111) at normal incidence was measured. As the incident energy is raised, a dramatic increase in the fraction of energy transferred to the surface, a shift of the rotational rainbow to higher rotational energy, and a significant increase in the amount of angular momentum alignment in the scattered molecules were observed. In addition, the alignment versus J distribution exhibits positive curvature for CO at all incident energies. The results are consistent with (1) the effect of the surface phonons and/or physisorption well on the final energy of the scattered molecules being small except at the lowest incident energy; (2) the large ∂V/∂θ being the primary source of the greater rotational excitation seen for CO compared to N2scattered from Ag(111); and (3) the corrugated attractive portion of the CO/Ag(111) potential being primarily responsible for the modest alignment of CO at low incident energy.