Electronic quenching of OH A 2Σ+ radicals in single collision events with H2 and D2: a comprehensive quantum state distribution of the OH X 2Π products

Abstract

A pump–probe laser-induced fluorescence technique has been used to examine the nascent OH X ²Π product state distribution arising from non-reactive quenching of electronically excited OH A ²Σ⁺ by molecular hydrogen and deuterium under single-collision conditions. The OH X ²Π products were detected in v″ = 0, 1 and 2; the distribution peaks in v″ = 0 and decreases monotonically with increasing vibrational excitation. In all vibrational levels probed, the OH X ²Π products are found to be highly rotationally excited, the distribution peaking at N″ = 15 when H₂ was used as the collision partner and N″ = 17 for D₂. A marked propensity for production of Π(A′) Λ-doublet levels was observed, while both OH X ²Π spin–orbit manifolds were equally populated. These observations are interpreted as dynamical signatures of the nonadiabatic passage of the OH + H₂/D₂ system through the seams of conical intersection that couple the excited state (2 ²A′) and ground state (1 ²A′) surfaces.