Spin-dependent reactivity and spin-flipping dynamics in O atom scattering from graphite

The formation of two-electron chemical bonds requires the alignment of spins; hence, it is well established for gas phase reactions that changing a molecule's electronic spin-state can dramatically alter its reactivity. For reactions occurring at surfaces, which are of great interest to, among others, heterogeneous catalysis, there is an absence of definitive state-to-state experiments capable of observing spin conservation and the role of electronic spin in surface chemistry remains controversial. Here, we use a novel incoming/outoing correlation ion-imaging technique to perform scattering experiments for O(³P) and O(¹D) atoms colliding at a graphite surface, in which the initial spin-state distribution is controlled and the final spin-states determined. We demonstrate O(¹D) is much more reactive with graphite than O(³P). We also identify electronically nonadiabatic pathways whereby incident O(¹D) is quenched to O(³P) that departs from the surface. With the help of molecular dynamics simulations carried out on high dimensional machine learning assisted first principles potential energy surfaces, we obtain a mechanistic understanding for this system: spin-forbidden transitions do occur, but with low probabilities.