TIME-RESOLVED LASER-EXCITED FLUORESCENCE AND PHOSPHORESCENCE IN GLYOXAL VAPOR

Author Institution: Department of Chemistry, University of IllinoisA Nitrogen-laser-pumped tunable liquid dye laser has been used to populate the first excited singlet state ($^{1}A_{u}$) of glyoxal. The collision-free lifetime of the $^{1}A_{u}$ state has been measured to be 2.24 $\mu$sec. The collisional efficiencies which have been measured for deactivation of the $^{1}A_{u}$ state appear to be relatively insensitive to the nature of the collision partner (He, Ar, Xe, $D_{z}$, $O_{z}$) suggesting little, if any, “heavy atom” effect. The collisional deactivation of the $^{1}A_{u}$ is accompanied by activation of the $^{1}A_{u}$ state, indicating considerable intersystem crossing. The lifetime of the $^{1}A_{u}$ state, 1.78 msec, is independent of rare gas pressure over the pressure range 0-70 Torr. However this triplet state is found to be effectively quenched by oxygen with a collisional rate of 3.15 $msec^{-1}$ $torr^{1}$. These preliminary experiments demonstrate the powerful potential of laser excitation as a tool for the study of excited-state dynamics