Wednesday, 16 May 2007 - 3:10 PM
012 (Pfahler Hall)
137

Electronic Quenching of OH A 2Σ+ Radicals in Single Collision Events with Molecular Hydrogen: Quantum State Distribution of the OH X2Π(v'' = 0,1,2) Products

Patricia A. Cleary1, Logan P. Dempsey1, Craig Murray1, Marsha I. Lester1, Jacek Klos2, and Millard H. Alexander2. (1) University of Pennsylvania, Philadelphia, PA, (2) University of Maryland, College Park, MD

Electronic quenching of OH A 2Σ+ by molecular hydrogen is known to be an efficient process. The process proceeds through conical intersection regions which produce nonreactive (OH X 2Π + H2) and reactive products (H2O + H). This work describes investigations into the nonreactive quenching channel. The experiments utilize a pump-probe scheme to determine the OH X 2Π population distribution following collisional quenching in a pulsed supersonic expansion. The pump laser excites OH A 2Σ+ (v′=0, N′=0), which has a significantly reduced lifetime due to quenching by H2. The probe laser monitors OH X 2Π (v″, N″) populations via laser-induced fluorescence on various A-X transitions under single-collision conditions. The experiments reveal a high degree of rotational excitation (N″) of the quenched OH X 2Π products observed in v″=0, 1 and 2 as well as a pronounced propensity for quenching into the Π(A') Λ-doublet level. The majority of the observed quenched OH X 2Π population lies in the lowest vibrational state (v″=0). The experimental results will be discussed with respect to multi-reference, configuration-interaction calculations aimed at exploring the topology of the relevant potential energy surfaces.

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