| Abstract
| - Phosphorescence and fluorescence excitation spectra of oxalylchloride (COCl)2 have been observed in asupersonic jet. Strong phosphorescence was observed for excitationof theband of theT13Au(nπ*) ←S0transition. From a vibrational analysis, it is shown that themolecule has C2h symmetry in theT1 excited stateas well as in the S0 ground state. Small splittingsdue to 35Cl and 37Cl isotopes werefound in several vibronicbands. For the excitation of the S1band, phosphorescence with a short lifetimewas observed, indicatingfast intersystem crossing in the origin level. In the higherenergy region, we could not observe phosphorescencebut only weak fluorescence. It suggests existence of activenonradiative processes such as internal conversionand predissociation in the vibrationally excited levels of theS1 state. A single-vibronic-level (SVL)dispersedphosphorescence spectrum has also been observed for the excitation ofthe T1 CO stretching band. Thespectrum was dominated by bands at the same wavelengths as those fortheexcitation. This clearlyshowsthat intramolecular vibrational redistribution (IVR) takes place withinthe long triplet lifetime. Althoughoxalyl chloride is assumed to be a “small molecule”, theradiationless transitions have been found to beefficient in both the T1 and S1states.
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