VIBRATIONAL RELAXATION IN THE $A^{2}\Sigma^{+}$ STATE OF OH

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1974

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Ohio State University

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Measurements have been made of vibrational energy transfer cross-sections $c_{v}$ for collisions of $A^{2}\Sigma^{+}$ OH with He, Ar, $H_{2}$, and $N_{2}$; The OH is selectively excited to specific rotational levels $N^{\prime}$ of the $v^{\prime} = 1$ level, using a frequency doubled tunable dye laser, and relaxes to the $v^{\prime} = 0$ level. The similarity of rotational and vibrational relaxation rates in $H_{2}$ and $N_{2}$ suggests the importance of $V \leftrightarrow R$ transfer in these molecules. It also permits the determination of $\sigma_{v}$ for individual $N^{\prime}$ levels of $V^{\prime}=1$; $\sigma_{v}$ is found to decrease as $N^{\prime}$ increases. The rotational distribution in $v^{\prime} = 0$ is nearly thermal, with no evidence of transfer into those levels resonant with the pumped level in $v^{\prime} =1$. Values of $\sigma_{v}$ for the $N^{\prime}=3$ level are(in {\AA}$^{2}$: He, $0.08 \pm 0.02$; $0.32 \pm 0.04$; $H_{2}$, $6 \pm 1$; $N_{2}$, $15 \pm 2$.

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This research was supported by the National Science Foundation.
Author Institution: Department of Chemistry, University of Wisconsin

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