MAPPING THE $OH + CO \leftrightarrow HOCO$ REACTION PATHWAY THROUGH INFRARED SPECTROSCOPY OF THE OH-CO REACTANT COMPLEX
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Date
2001
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Publisher
Ohio State University
Abstract
A hydrogen-bonded OH-CO complex has been identified along the reaction coordinate for the $OH + CO \leftrightarrow HOCO \rightarrow H + CO_{2}$ reaction. The vibrational spectrum of the OH-CO complex has been examined in the OH overtone region at $1.4 \mu m$ using infrared action spectroscopy, which relies on detection of $OH (v = 1)$ fragments from vibrational predissociation by laser-induced fluorescence. The observed infrared spectrum of OH-CO consists of the pure OH overtone band at $6941.7 cm^{-1}$ and combination bands involving the simultaneous excitation of OH stretch and intermolecular vibrations, which appear 50 to $250 cm^{-1}$ higher in energy than the pure overtone. The rotational structure of the pure overtone band is indicative of a parallel transition of a linear OH-CO complex having a $P = 3/2$ projection of the total angular momentum on the intermolecular axis, which arises from the unquenched electronic angular momentum of OH. The OH-CO binding energy, $D_{0} \leq 430 cm^{-1}$, is also established from the quantum state distribution of the OH fragments following pure overtone excitation. The strongest combination bands with 51.1, 57.1, and $247.3 cm^{-1}$ of intermolecular energy are attributed to geared bend and H-atom bend excitation, which are the modes that drive the transformation from OH-CO to HOCO. These combination bands exhibit rotational structures that are characteristic of perpendicular transitions $(\Delta P = \pm 1)$ to states with vibrational angular momentum from the bending motions of the complex. A complete analysis of the experimental results promises to yield a spectroscopic quality characterization of the $OH + CO \rightarrow HOCO$ reaction pathway. $^{a}$Permanant address: Department of Chemistry, Amherst College, Amherst, MA 01002-5000
Description
Author Institution: University of Pennsylvania; Department of Chemistry, University of Pennsylvania