Effects of nonzero correlation time of system–reservoir interaction on the excitation profiles of second-order optical processes in β-carotene

Excitation spectra for narrow Raman lines and a broad luminescence band have been measured in β-carotene in isopentane at 177 K over a wide spectral range on the low-energy side of the 1Ag–1Bu absorption band. The result has been found to be well explained by a stochastic theory that takes into account the finiteness of the correlation time for the intermediate-state interaction. Various parameters, such as the magnitude and the rate of the energy modulation in the intermediate state, have been determined from the analysis of the excitation profiles. The parameter values obtained indicate that the intermediate-state interaction is far from the motional-narrowing limit in this system.