Rotationally inelastic gas–surface scattering: HCl from Au(111)

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Abstract
A quantum-resolved molecular beam–surface scattering study of HCl scattered from Au(111) is described. The HCl is detected in a quantum-resolved manner via (2+1) resonant enhanced multiphoton ionization (REMPI). Greater than 85% of the incident HCl molecules are in a single-quantum state (v=0, J=0) with a narrow velocity distribution (Δυ/υ<0.10). The scattered HCl is strongly peaked about the specular angle, and both its final velocity and rotational distributions are indicative of direct inelastic scattering. The scattered rotational distributions exhibit features characteristic of rotational rainbows and have a mean rotational energy that displays a bilinear dependence upon the incident normal kinetic energy and surface temperature. The final velocity distributions are largely insensitive to the rotational level and indicate that the energy loss to phonons is small (<20%). Analysis of the scattered data indicates an orientation-averaged attractive well depth of ∼5 kcal/mol for the HCl–Au(111) interaction.