Emission polarization in the S3 state of CS2 vapor as a probe of predissociation: Consideration of the finite bandwidth of the incident field

Depolarization ratios of resonantly excited light emission have been measured for low pressure CS2 vapor at room temperature in three distinct spectral regions on resonance with the intense predissociative S3←S0 electronic transition. While the emission spectra have the general appearance of resonance Raman spectra, the non-negligible bandwidth of the laser source relative to the rovibronic linewidths implies that the emission should properly be described as a combination of incoherent ‘‘fluorescence’’ and true Raman processes. The effect on the emission polarization of a finite excitation spectral bandwidth arising from phase fluctuations in the incident radiation field is developed in detail. The depolarization dispersion curves are analyzed to estimate the J-averaged excited state lifetimes, which vary from 1.5 ps near 212 nm to 0.44 ps near 200 nm. The predissociation lifetimes appear to be at most weakly dependent on J based on analysis of the emission rotational band contours. Some discrepancies between the present lifetime estimates and those previously obtained through photofragment anisotropy measurements are discussed.