HIGH-TEMPERATURE QUENCHING OF $CH (A^{2}\Delta,v'=0)$
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Date
1986
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Ohio State University
Abstract
Quenching rate constants for the $A^{2}\Delta v'=0$ state of CH have been obtained in a laser pyrolysis/laser fluorescene (LP/LF) system for a variety of collision partners. In the LP/LF cell, a $CO_{2}$ laser pulse irradiates a gas mixture of $SF_{6}, CF_{4}$, and $CH_{4}$ and quencher, rapidly heating the system to 1300 K. Abstraction of H atoms from $CH_{4}$ by F atoms (produced by the thermal decomposition of $SF_{6}$) generates CH radicals. Ground state CH radicals are excited to the $A^{2}\Delta$ state by a pulsed dye laser and the fluorescence lifetime is measured as a function of quencher pressure. The cross sections $(A^{2})$ at 1300 K are: $$\begin{array}{cccccccccc}CO &O_{2}&H_{2}&D_{2}&N_{2}&N_{2}O&CO_{2}&NH_{3}\\\hline8.5\pm 1.0 &2.8 \pm 0.4 &3.6 \pm 0.4 &3.8 \pm 0.4 &1.3 \pm 0.2 &5.5 \pm 0.7 &2.2 \pm 0.3 &22.5 \pm 3.0\\\end{array}$$ These cross sections will be compared with those measured in this laboratory for NH and CH at high temperature $(>1000K)$ and also with results from room temperature CH quenching experiments which are in progress.
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Supported by the Physical Sciences Department of the Gas Research Institutes Address of Authors: Molecular Physics Department, SRI International, Menlo Park, CA 94025
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