VIBRONIC ASSIGNMENTS IN THE $^{1}A_{u}-^{1}A_{g}$ ABSORPTION SPECTRUM OF GLYOXAL BY TIME-RESOLVED SVL FLUORESCENCE

Abstract

Fluorescence spectra from single vibronic levels (SVL) In glyoxal vapor have been analysed in order to (1) experimentally establish the vibrational modes populated during absorption transitions and (2) provide information about excited-state structure through the analyses of Franck-Condon factors. Since such spectra are comprised of ground-state vibrational frequencies which are well established from infrared and Raman spectroscopy, these data can often provide unique identification of absorption transitions. Time-resolved SVL (TRSVL) techniques utilize box car integration and pulsed laser excitation to observe emission before a significant degree of collisional perturbation can redistribute excited-state energy to vibrational modes not initially-populated in $absorption^{1}$ TRSVL techniques have been used to reveal the activity of $\nu_{6}$ for the first time and to confirm more than twenty other vibronic transitions. A low resolution analysis of fluorescence band contours is included in this work. A Franck-Condon analysis of these fluorescence spectra has also been performed and provides new information about the geometry of the $^{1}A_{u}$ state.