ROTATIONAL RELAXATION IN THE $^{1}A_{u}$ STATE OF GLYOXAL VAPOR
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Date
1975
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Ohio State University
Abstract
$Ar^{+}$ - laser excitation has been used to pump several vibrational bands in the $^{1}A_{u} \leftarrow ^{1}A_{g}$ electronic transition of glyoxal. The laser band-width restricts each excitation to $\approx 10-15$ rotational levels of the $^{1}A_{u}$ state. Fluorescence after excitation to the level ${v^{\prime}}^{7} = 1$ shows features due to yibrational relaxation to the $0^\circ$ state at pressures as low as $5 \times 10^{-4}$ Torr. At this pressure no appreciable rotational relaxation can be observed within the $7_{1}$ state but the rotational structure of the $0^\circ$ O emission band indicates that rotational quantum number changes have accompanied vibrational relaxation. Strong propensity rules for $\Delta K$ are observed. Fluorescence after pumping the aero point level directly shows little evidence of rotational equilibration even at pressures up to $10^{-2}$ Torr. The course of rotational energy transfer has been followed as a function of pressure. Collision-induced intersystem crossing is found to compete effectively with rotational and vibrational relaxation.
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Author Institution: Department of Chemistry, Indiana University