Emission spectroscopy and excited-state dynamics of chromyl-chloride vapor

A tunable dye laser has been used to excite single vibronic features in the low-pressure vapor of CrO₂Cl₂. The fluorescence spectrum, fluorescence excitation spectrum and time-resolved fluorescence decay are discussed. It is shown that the active ν′₄ and ν″₄ modes are the same frequency in the gas phase, thus collapsing the sequence congestion normally observed in gas-phase spectra. This degeneracy makes impossible the excitation of single vibronic levels. It is shown that the fluorescence lifetime of the excited state in all except the vibrationally cold level is severely shortened by unimolecular radiationless decay. This radiationless rate is strongly dependent upon the partitioning of energy into various excited-state modes. The radiative lifetime of the vibrationally cold excited state is (1.34 ± 0.08) μs and the apparent bimolecular quenching rate is (5.9 ± 0.2) × 10^?10 cm³/molecules. No evidence of emission from the lowest-energy excited electronic state recently reported by Spoliti [J. Mol. Spectrosc. 52 (1973) 146] is observed.