Energy Transfer and Thermal Accommodation in Ozone Scattering from a Perfluorinated Self-Assembled Monolayer

Abstract

A modification of the energy transfer model recently proposed by two of us (ref 4) is tested in this work by an extensive comparison with the simulation results for O3 scattering from a perfluorinated self-assembled monolayer (F-SAM) as well as with previous NO + FSAM and Ar + F-SAM scattering results. The model fits very well the trajectory data over a ∼103-fold of incident energies. The percentage of energy transferred to the surface, predicted by the model at high incident energies, decreases with the number of degrees of freedom of the projectile because they compete with the surface degrees of freedom as possible destinations of the incident energy. The distributions of the scattered ozone molecules over translational and rotational states show a low-energy component characterized by a Maxwell–Boltzmann (MB) distribution at the surface temperature that survives at the highest collision energies. The dependence of the fraction of the MB component on the incident energy is an exponential decay function and the rate of decay is similar for the rotational and translational distributions. A non-negligible number of the O3 + F-SAM trajectories that penetrate the surface at high energies have very long residence times (longer than the simulation time), which enables thermal accommodation of the rotational and translational degrees of freedom. A new method to categorize the O3 + F-SAM trajectories, based on the residence time, shows that, at very low incident energies (<10 kcal/mol), thermal accommodation can be achieved in a single collision event.