On the Influence of Rotational Motion of Oxygen Molecules on the Scattering from Graphite Surfaces

A new analytical potential energy surface is proposed to investigate, by semiclassical molecular dynamics calculations, the scattering of O2 molecules in well-defined initial roto-vibrational (vi, ji) states from graphite under a variety of conditions of applied interest. The reaction dynamics appears to be dominated by the coupling between translational and rotational internal degrees of freedom of molecule, that, at low-medium collision energies, can be also triggered by the energy exchange with the surface phonons. The final states (vf, jf) of backscattered molecules are characterized and carefully analyzed. Most important results are the following: (1) after the interaction with the surface, molecules are backscattered mainly in a direction very close to the specular one; (2) vi is preserved, except for high initial vibrational states; (3) the surface temperature plays a minor role; and (4) the final jf states exhibit non-Boltzmann distributions with the main peak nearby jf = ji and a secondary maximum at very high jf. Moreover, the features of rotational distributions suggest a close correlation between the initial rotational configuration of impinging molecules and the final state achieved after the scattering. These findings, complementary to those from molecular beam experiments, cast light on relevant selectivities in elastic and inelastic collision events that control the stereodynamics of several elementary processes occurring both in gaseous and condensed phases for low energy (as those meet in the interstellar medium) as well as for high energy (as those of interest for aerospace applications).