Orientation and energy dependence of NO scattering from Pt(111)

A classical molecular dynamics study is applied to simulate the scattering of NO from Pt(111) in the energy range of 0.3-1 eV. The solid consists of a large number of crystal atoms that interact via an anharmonic nearest-neighbor potential. The NO-Pt(111) interaction potential is constructed as a pairwise additive potential with a well depth of 1 eV for the N end of the molecule towards the surface and purely repulsive for the O end. The in-plane scattering results obtained with this model potential are compared with recent experiments for NO-Pt(111). The angular intensity distributions, the final translational energy, as well as the rotational energy distributions with the corresponding alignment are in qualitative agreement with those experimental results. A detailed examination of the collision dynamics shows that multiple collisions with the surface results predominantly in superspecular scattering, The rotational angular momentum of the scattered molecules exhibits a preference for cartwheeling alignment and the rotational energy distributions for specular and normal exit angles can be described with a Boltzmann distribution, whereas for grazing exit angles they are distinctly non-Boltzmann. The latter structure results from a cutoff in the rotational excitation by the attraction of the well. The high rotational excitation clearly originates from molecules that initially are oriented with the O end towards the surface, whereas for the low rotational excitation this orientation preference disappears. (C) 1996 American Institute of Physics.