VIBRATIONAL PREDISSOCIATION DYNAMICS OF THE HYDROGEN BONDED $OH-C_{2}H_{2}$ REACTANT COMPLEX
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Date
2003
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Publisher
Ohio State University
Abstract
Reaction of acetylene with the hydroxyl radical is the only significant loss of this alkyene in the atmosphere. Previous studies have shown the reaction to have pressure dependent kinetics and several different reaction intermediates and products. Under atmospheric conditions, the rate of reaction may be influenced by a hydrogen bonded adduct between the two partners in the entrance channel to reaction. The infrared action spectrum of this complex between $C_{2}H_{2}$ and OH has been recorded in the OH overtone region near $1.4 {\mu}m$. The rotationally resolved OH overtone band is centered at $6885.6 cm^{-1}$, and analysis reveals a T-shaped, $\pi$-hydrogen bonded structure for the $OH-C_{2}H_{2}$ complex. Following IR excitation, the complex can undergo vibrational predissociation or reaction via addition or hydrogen abstraction pathways. Vibrational predissociation produces OH fragments which are detected by laser induced fluorescence on the OH A-X (0,1) transition. The highest observed OH ($v = 1$) product rotational state, $j_{OH}=23/2, \omega=3/2$, resulting from a vibration to rotation/translation process, allows for determination of an upper limit of the binding energy, $D_{0} \leq 995 cm^{-1}$. The OH fragments also strongly populate $j_{OH}=9/2$ and 11/2 states, indicating a vibration-vibration channel likely arising from energy transfer to the $\nu_{2}$ C-C stretch of the acetylene partner.
Description
Author Institution: Department of Chemistry, University of Pennsylvania