Knowledge Bank

Single vibronic level excitation of oxalyl fluoride $(C2O2F2)$ near the origin $(\lambda \ge 3000${\AA}) of the first excited singlet state by a tunable frequency doubled dye laser gives rise to fluorescence. The zero-pressure fluorescence lifetime of these levels $(\sim 22\mu sec)$ is probably purely radiative. The bimolecular self-quenching rate constants for these radiative levels are on the order of $20$ x $106sec-1Torr-1$. This rate, which is dominated by collision-induced intersystem crossing, gives rise to intense phosphorescence with a lifetime of several milliseconds. Strong phosphorescence is still evident at pressures below 10 mTorr. Scanning of the fluorescence excitation spectrum demonstrates that only levels near the origin result in fluorescence. The unimolecular radiationless process probably corresponds to the onset of predissociation giving two FCO radicals in the primary photochemical process. The energy dependence of this process has been mapped out. Experimental details and the radiative and radiationless processes will be discussed.