Oxygen Adsorption on beta-Cristobalite Polymorph: Ab Initio Modelling and Semiclassical Time-Dependent Dynamics

he adsorption dynamics of atomic oxygen on a model beta-cristobalite silica surface has been studied by combining ab initio electronic structure calculations with a molecular dynamics semiclassical approach. We have evaluated the interaction potential of atomic and molecular oxygen interacting with an active Si site of a model beta-cristobalite surface by performing DFT electronic structure calculations. As expected, 0 is strongly chemisorbed, E(b) = 5.57 eV, whereas molecular oxygen can be weakly adsorbed with a high-energy barrier to the adsorption state of similar to 2 eV. The binding energies calculated for silica clusters of different sizes have revealed the local nature of the O,O(2)-silica interaction. Semiclassical collision dynamic calculations show that O is mainly adsorbed in single-bounce Collisions, with a smaller probability for adsorption via a multicollision mechanism. The probability for Adsorption/desorption (reflected) collisions at the three impact energies is small but not negligible at the higher energy considered in the trajectory calculations, about P(r) = 0.2 at E(kin) = 0.8 eV. The Calculations give evidence of a complex multiphorion excitation-deexcitation mechanism underlying tile dynamics of stable adsorption and inelastic reflection collisions.