The steric effect in surface scattering of oriented molecules: An optical model interpretation

The new experimental observation by Bernstein and coworkers of strong orientation dependence in the scattering of molecules by graphite are interpreted by introducing a scattering theoretic optical model. The theory can account for the surface temperature dependence of the sticking probability, the sign of the steric effect being different for different molecules, the dependence of the steric effect on orientation and on surface temperature and the sign of this dependence. Explicit predictions are made for the dependence of the steric effect on collision energy. The prime information provided by the analysis is the orientation dependence of the molecule-surface interaction.