Collisional Quenching of OH Radicals: Dynamical Outcomes

The nascent OH X²Î  product state distributions arising from collisional quenching of electronically excited OH A²Î£+ by several molecular partners have been determined using a pump-probe technique. For H₂ and N₂ collision partners, the majority of OH X²Î  products are observed in their lowest vibrational level, v″=0, with significantly less population in v″=1. The OH (v″=0) products are generated with a substantial degree of rotational excitation, peaking around N″=15 with H₂ as the collision partner and N″=18 with N₂. Complementary measurements of the branching fraction into OH ²Î  product states demonstrate that reaction is the dominant decay pathway for quenching of OH A²Î£+ by H₂, while nonreactive quenching is the dominant pathway for N₂. These observations are discussed in the context of theoretical calculations that examine the topography of the conical intersections which couple the electronically excited and ground state potential energy surfaces. The experimental observables are interpreted as dynamical signatures of nonadiabatic passage through the conical intersection regions responsible for quenching in both systems.

For more information contact Prof. Christine Payne (404-385-3125).