AACP Seminar Series - Prof. Marsha Lester, University of Pennsylvania

Collisional Quenching of OH Radicals: Dynamical Outcomes

The nascent OH X2Π product state distributions arising from collisional quenching of electronically excited OH A2Σ+ by several molecular partners have been determined using a pump-probe technique. For H2 and N2 collision partners, the majority of OH X2Π 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 2Π product states demonstrate that reaction is the dominant decay pathway for quenching of OH A2Σ+ 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).