Collisional quenching of OH A 2Σ+ radicals by H2: Dynamical signatures of passage through conical intersections

PHYS 33

Logan P. Dempsey, Craig Murray, crmurray@sas.upenn.edu, Patricia A. Cleary, and Marsha I Lester, milester@sas.upenn.edu. Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104-6323
The collisional quenching of OH A 2Σ+ radicals by H2 is examined to determine the nascent OH X 2Π product distribution from nonreactive quenching as well as the partitioning between nonreactive and reactive pathways. The OH X 2Π vibrational distribution peaks in v″=0 and decreases monotonically with increasing vibrational excitation. The OH X 2Π products are found to be highly rotationally excited with a marked propensity for production of OH Π(A′) λ-doublet levels. A comparison of the population prepared in the excited OH A 2Σ+ state with that produced in the OH X 2Π ground state reveals that only a small fraction of the products, less than 15%, arise from non-reactive quenching. These observations are interpreted as new dynamical signatures of passage through seams of conical intersection that couple the excited state potential for OH A 2Σ+ + H2 with OH X 2Π + H2 and H2O + H products.