ROTATIONAL-STATE SPECIFIC ELECTRONIC QUENCHING OF OH $(A^{2}\Sigma^{+}, v^{\prime}=0)^{\ast}$
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Date
1984
Authors
Copeland, Richard A.
Dyer, M. J.
Crosley, David R.
Journal Title
Journal ISSN
Volume Title
Publisher
Ohio State University
Abstract
Electronic quenching rate constants for collisions of OH $(A^{2}\Sigma^{+}, v^{\prime}=0)$ with a variety of collision partners were measured for individual rotational levels using laser-induced fluorescence. Colliders studied to date are $H_{2}O, O_{2}, N_{2}, H_{2}, D_{2}, CH_{4}, D_{2}O, N_{2}O, SF_{6}, CF_{4}$ and $CCl_{4}$. The large rotational energy spacing, along with the generally rapid electronic quenching of OH, permitted the extraction of these rotation-state-specific rate constants from the pressure dependence (0-100 mtorr) of the temporal evolution of the total fluorescence. There exists a significant decrease (up to 60\% for $N^{\prime}=7$ compared to $N^{\prime}=0$) in electronic quenching with increasing rotational level for most collision partners, even though the absolute magnitude of the rate constant varies more than a factor of 30 over the set. $SF_{6}$ and $CF_{4}$ are inefficient electronic quenchers but efficient at rotational energy transfer, masking any rotational level effect. The substitution of $D_{2}$ for $H_{2}$ and $D_{2}O$ for $H_{2}O$, thereby changing the vibrational and rotational structure of the quencher, caused a negligible change in the quenching cross sections. Collisions of $OD(A^{2}\Sigma^{+}, v^{\prime}=0)$ with $D_{2}O$ show similar effects. This effect was first observed by McDermid and Laudenslager for $N_{2}$ and $O_{2\cdot}^{1}$ Its persistence throughout the numerous collision partners suggests that electronic energy transfer in this system, where long range forces are $important,^{2}$ is sensitive to dynamical effects caused by the internal state of the OH which is quenched in the collision.
Description
$^{\ast}$ Supported by the National Aeronautics and Space Administration, Contract No. NASI-16956. $^{1}$ I.S. McDermid and J.B. Laudenslager, J. Chem. Phys. 76, 1814 (1982). $^{2}$ P.W. Fairchild, G.P. Smith, and D.R. Crosley, J. Chem. Phys. 79, 1795 (1983).
Author Institution: Molecular Physics Department, SRI International
Author Institution: Molecular Physics Department, SRI International