SINGLE ROTATIONAL LEVEL FLUORESCENCE SPECTROSCOPY AND ROTATIONAL RELAXATION IN THE $S_{1}(^{1}A_{u})$ OF GLYOXAL

Author Institution: Department of Chemistry, Indiana UniversityResolved emission from a single rotational level or from a small selection of rotational levels in the zero point level of $S_{1}$ glyoxal has been obtained after pumping with the 4545.05 {\AA} line of an $Ar^{+}$ laser in single mode operation (line width $\leq 10^{-4}$ all $cm^{-1}$ tunable over $0.15 cm^{-1})$. The rotational structure of vibrational bands in emission is completely consistent with Ramsay’s analysis of absorption. A single rotational level fluorescence excitation experiment can be done by monitoring fluorescence intensity at one of the unique positions of emission from a single rotational level while tuning the laser. We show as an example of this how several absorption bands overlapping by Doppler widths can each be separated and characterized individually. These techniques give an absolutely secure understanding of the absorption and emission spectroscopy associated with the laser excitation, and set the stage for studies of collisional rotation relaxation in the excited state. Cross sections about four times hard sphere are found for collisions with ground state glyoxal. Strong propensity for small $\Delta K$ and $\Delta J$ changes on relaxation are absent