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

It has been indisputably demonstrated that a molecule’s electronic spin can dramatically influence its reactivity in gas phase reactions; but, clear evidence of spin selection rules in surface chemistry, while of widespread interest, remains elusive. State-to-state experiments that seek to observe the conservation of spin in surface chemical reactions are nearly unknown. In this work, we report scattering experiments for O(³P, ¹D) atoms colliding at a graphite surface, where the initial and final spin-states are determined. We clearly identify electronically nonadiabatic pathways where O(¹D) is quenched to O(³P), releasing excess translational energy. Molecular dynamics simulations help to confirm spin-selective collision and reveal the mechanism of spin flipping, which is consistent with a ~100 fs spin relaxation timescale—sufficiently long to enable spin-selective chemistry, as suggested by the enhanced sticking probability of O(¹D) relative to O(³P) at graphite. The experiments are made possible by a novel pump-probe ion-imaging technique that yields high resolution scattering data, even when using spin-state enriched beams with poorly defined velocity distributions.