# COLLISIONAL QUENCHING OF OH ${A^2\Sigma^+}$ BY H$_2$: LIFETIMES AND METHODS FOR PROBING THE NONREACTIVE PRODUCT CHANNEL

Please use this identifier to cite or link to this item: http://hdl.handle.net/1811/30739

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 Title: COLLISIONAL QUENCHING OF OH ${A^2\Sigma^+}$ BY H$_2$: LIFETIMES AND METHODS FOR PROBING THE NONREACTIVE PRODUCT CHANNEL Creators: Dempsey, Logan P.; Cleary, Patricia A.; Murray, Craig; Lester, Marsha I. Issue Date: 2006 Publisher: Ohio State University Abstract: Collisional quenching of electronically excited OH ${A^2\Sigma^+}$ radicals by molecular hydrogen is known to be an efficient process. Quenching can proceed through a reactive channel, producing water and atomic hydrogen, or through a nonreactive channel. The goal of this work is to study the outcome of the nonreactive quenching channel, and thereby extract information about the dynamical pathways that lead to quenching. A pump-probe scheme is utilized to determine the OH ${X^2\Pi}$ population distribution following collisional quenching in a pulsed supersonic expansion. The pump laser excites OH ${A^2\Sigma^+}$ ${(v^{\prime}=0, N^{\prime}=0)}$, resulting in a significantly reduced lifetime due to quenching. The probe laser monitors the OH ${X^2\Pi}$ ${(v^{\prime \prime}, J^{\prime \prime})}$ population via laser-induced fluorescence (LIF) on various ${A-X}$ transitions. To convert observed LIF intensities to a population distribution, it is necessary to account for the fluorescence quantum yield and lifetime of the emitting state. Quenching lifetimes for OH ${A^2\Sigma^+}$ radicals are measured at a temperature of $\sim$50 K and fit to a single exponential decay. Lifetimes of OH ${A^2\Sigma^+}$ ${(v^{\prime}=0, N^{\prime})}$ show a dramatic increase with rotational level ${N^{\prime}}$, corresponding to a decrease in quenching efficiency. The experimental lifetimes are used to extract pseudo first-order rate constants for quenching as a function of ${N^{\prime}}$ under these conditions. Description: Author Institution: Department of Chemistry, University of Pennsylvania, Philadelphia, PA, 19104 URI: http://hdl.handle.net/1811/30739 Other Identifiers: 2006-TJ-02