Non-adiabatic effects in the dissociative adsorption of O2 on aluminum (111) surfaces

Abstract

The low sticking probability for thermal oxygen molecules at aluminum(111) has recently been related to spin selection rules, which hinder transitions from the initial oxygen gas-phase triplet state to the singlet state of the adsorbed O atoms. A constrained DFT approach was employed to compute potential energy surfaces (PESs) of oxygen in different spin-configurations both with and without charge transfer from the surface, and the experimental sticking probability was qualitativly reproduced when restricting the oxygen molecule to motion on the spin-triplet PES only. Here, these studies are extended by considering the dissociation dynamics on multiple spin PESs, allowing transitions between them within Tully’s fewest-switches algorithm. The required non-adiabatic coupling elements have been derived in an ab initio fashion from the comparison between adiabatic and constrained DFT PESs. Within this framework, we obtain both good agreement with experiment for the fundamental features of the system and deeper insight on more peculiar characteristics of the dynamics, allowing us to propose experiments for the validation of our approach.