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

A pump-probe laser-induced fluorescence technique has been used to examine the nascent OH X (2)Pi product state distribution arising from non-reactive quenching of electronically excited OH A (2)Sigma(+) by molecular hydrogen and deuterium under single-collision conditions. The OH X (2)Pi 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 (2)Pi products are found to be highly rotationally excited, the distribution peaking at N '' = 15 when H-2 was used as the collision partner and N '' = 17 for D-2. A marked propensity for production of Pi(A') A-doublet levels was observed, while both OH X (2)Pi spin-orbit manifolds were equally populated. These observations are interpreted as dynamical signatures of the nonadiabatic passage of the OH + H-2/D-2 system through the seams of conical intersection that couple the excited state (2 2 A') and around state (1 (2)A') surfaces.