Collisional quenching of OH A 2Σ+ by molecular hydrogen: OH X 2Π Product state distribution and branching between reactive and nonreactive pathways

PHYS 584

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 quantum state distribution of OH X 2Π radicals generated by electronic quenching of OH A 2Σ+ radicals with H2 is investigated using a pump-probe scheme. The pump laser excites OH A 2Σ+(v′=0, N′=0), which has a significantly reduced fluorescence lifetime due to quenching. The probe laser monitors OH X 2Π(v″, N″) population via laser-induced fluorescence on various A-X transitions under single-collision conditions. Experiments reveal a high degree of rotational excitation (N″=0), minimal vibrational excitation (v″), and a pronounced propensity for quenching into Π(A′) Λ-doublet levels. Additional measurements compare emission from the initially pumped level with the laser-induced fluorescence signal from one of most populated product states. These measurements, with the OH X 2Π quantum state distribution are used to determine the branching between reactive and nonreactive quenching pathways. The reactive quenching pathway is found to be the dominant channel (~85%).