QUENCHING OF THE $A^{2}\Sigma^{+}$ STATE OF OH AT $\sim$1100
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Date
1983
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Publisher
Ohio State University
Abstract
K Rate constants for collisional quenching of the $v^{\prime}=0$ level of the $A^{2}\Sigma^{+}$ state of the OH molecule have been measured at temperatures in the range 1000-1400 K. The OH was produced at these temperatures by a laser pyrolysis $method.^{1}$ In which a mixture of $SF_{6}, H_{2}O_{2}$ and the collision partner was irradiated by a pulsed $CO_{2}$ laser. The $SF_{6}$ absorbed the infrared radiations, rapidly heating the mixture and pyrolyzing the peroxide to OH radicals. The OH was pumped to the $N^{\prime}=6, J^{\prime}=6 1/2, v^{\prime}=0$ level of the $A^{2}\Sigma^{+}$ state by a 10 nsec-long frequency doubled dye laser pulse fired $30 \mu sec$ after the $CO_{2}$ laser. Quenching rate constants were measured by the added gas pressure dependence of the fluorescence decay time. The results, given as thermally averaged cross sections $(A^{2})$ at 1100 K are: [FIGURE] No significant temperature dependence was observed over the limited range covered, in agreement with expectations. However, the values are lower than room temperature literature values (which exist for colliders marked with an asterisk), except for $H_{2}$. The values for $N_{2}$ and $SF_{6}$ are conspicuously low. Cross sections have been calculated with a collision complex mode, were multipole attractive forces and a repulsive rotational barrier dominate the potential, a reformulation of an approach used for $SO_{2}.^{2}$ The experimental results for the first eight of the collision partners listed agree well $(\pm25\%)$ with the calculation, assuming 0.45 probability of quenching per capture collision. This research was supported by the U.S Army Research Office. $^{1}$P.W. Fairchild, G. P. Smith and D. R. Crosley, Nineteenth Symposium (International) on Combustion, The Combustion Institute, Pittsburg, 1983, in press. $^{2}$D.L. Holtermann, E.K.C. Lee and R. Nanes, J. Chem. Phys. 77, 5327 (1982).
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Author Institution: Molecular Physics Laboratory, SRI International