The use of van der Waals molecules to detect a mode selective nonradiative process in chromyl chloride

摘要

A free jet expansion was used to form van der Waals complexes of helium and chromyl chloride of the type CrO2Cl2ndash;He(x),x= 1,2,... The vibronic bands of both the complex and the corresponding parent molecule have been excited using a tunable cw dye laser, and the fluorescence excitation spectra were recorded. The lifetimes of the complexes were measured and were found to be in the range 11ndash;121 ps. The complexes undergo vibrational predissociation after excitation. For the van der Waals molecules we have evidence of competition between the vibrational predissociation and a nonradiative process in the CrO2Cl2portion of the complex. The fluorescence intensity of a vibronic band of the complex relative to the corresponding band of the uncomplexed parent molecule shows that there is a mode selective nonradiative process in the1B1excited state of CrO2Cl2. The cross section for this nonradiative process increases with increasing excitation of the ngr;4mode, the CrCl2bend. A kinetic scheme is presented to interpret these observations, and the utility of this effect to measure vibrational predissociation rates in polyatomic moleculendash;rare gas van der Waals complexes is discussed.