RADIATIVE AND NONRADIATIVE PROCESSES IN THE EXCITED-STATES OF JET-COOLED OXALYL CHLORIDE

Phosphorescence and fluorescence excitation spectra of oxalyl chloride (COCl)(2) have been observed in a supersonic jet. Strong phosphoresce nce was observed for excitation of the O-0(0) band of the T(1)(3)A(u)( n pi)<-- S-0 transition. From a vibrational analysis, it is shown tha t the molecule has C-2k symmetry in the T-I excited state as well as i n the S-0 ground state. Small splittings due to Cl-35 and Cl-37 isotop es were found in several vibronic bands. For the excitation of the S-1 O-0(0) band, phosphorescence with a short lifetime was observed, indi cating fast intersystem crossing in the origin level. In the higher en ergy region, we could not observe phosphorescence but only weak fluore scence, It suggests existence of active nonradiative processes such as internal conversion and predissociation in the vibrationally excited levels of the S-1 state. A single-vibronic-level (SVL) dispersed phosp horescence spectrum has also been observed for the excitation of the T -1 C=O stretching band. The spectrum was dominated by bands at the sam e wavelengths as those for the O-0(0) excitation. This clearly shows t hat intramolecular vibrational redistribution (IVR) takes place within the long triplet lifetime. Although oxalyl chloride is assumed to be a ''small molecule'', the radiationless transitions have been found to be efficient in both the T-1 and S-1 states.