Angular distributions in stimulated desorption: photodesorption of ammonia from a Cu(111) surface

The angular distributions of flux and mean translational energy in stimulated desorption containe valuable information about the influence of substrate corrugation on the desorption dynamics. We present a simple model which predicts angular distributions of desorbing neutrals if the particle momentum parallel to the surface is conserved during the desorption process. The model allows the calculation of the temperature dependence of angular distributions and the observed decrease in translational energy with increasing angle of desorption. For the photostimulated desorption of NH3 from Cu(111) at two sample temperatures our analysis shows that substrate corrugation has no significant influence on the angular flux distributions which are essentially broadened by thermal motions of the molecules within the surface plane, i.e. due to the frustrated translation.