TIME-RESOLVED FLUORESCENCE FROM SINGLE VIBRONIC LEVELS OF GLYOXAL

This research was supported by the National Science Foundation Grant GP-33666. W.C. Lineberger has been an Alfred P. Sloan Foundation fellow, 1972-74.Author Institution: Department of Chemistry and Joint Institute for Laboratory Astrophysics, University of Colorado BoulderA pulsed, tunable dye laser has been used to excite glyoxal vapor at pressures from 1 mTorr to 200 mTorr. The fluorescence is resolved through a spectrometer and time behavior studied with 100 nsec resolution. Quenching rate constants for the vibrationless levels of the first excited state of cis and trans-glyoxal have been measured with spectrometer resolution of several angstroms. Quenching of cis-glyoxal is found to be about two to three times faster than that of trans-glyoxal for a variety of collision partners. The rate constant for trans-glyoxal quenching the $vibrationless^{1}B_{1}$ level of cis-glyoxal is determined to be $1.40 \pm 0.05 \times 10^{-9}$ $cm^{3}$$sec^{-1}.$ The zero pressure extrapolated lifetime is $0.96 \pm 0.02 \mu$sec for cis-glyoxal compared to a value of $2.17 \pm 0.02 \mu$sec for the corresponding level of the trans-glyoxal $^{1}A_{u}$ state. Single vibronic levels of the $^{1}A_{u}$ state of trans-glyoxal were excited under collision free conditions and fluorescence from the directly excited level and other levels individually time resolved to study the transfer of energy among the levels of this state