Spin-dependent reactivity and spin-flipping dynamics in oxygen 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 during, among other processes, heterogeneous catalysis, there is an absence of definitive state-to-state experiments capable of observing spin conservation and therefore the role of electronic spin in surface chemistry remains controversial. Here we use an incoming/outgoing correlation ion imaging technique to perform scattering experiments for O(P-3) and O(D-1) atoms colliding with a graphite surface, in which the initial spin-state distribution is controlled and the final spin states determined. We demonstrate that O(D-1) is more reactive with graphite than O(P-3). We also identify electronically nonadiabatic pathways whereby incident O(D-1) is quenched to O(P-3), which 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.

Automated summary

The alignment of spins is essential for the formation of two-electron chemical bonds. While it is known that changing a molecule's electronic spin state can significantly impact its reactivity in gas-phase reactions, the role of electronic spin in surface chemistry remains controversial due to the absence of definitive state-to-state experiments. This study uses an incoming/outgoing correlation ion imaging technique to perform scattering experiments and demonstrates that O(D-1) is more reactive with graphite than O(P-3), also identifying electronically nonadiabatic pathways.