Electronic spectra and intramolecular dynamics of phenanthrene in a supersonic free jet

Abstract

The fluorescence excitation spectra and the fluorescence decays of phenanthrene-h10 and phenanthrene-d10 in a supersonic free jet have been measured with excitation across the S 0 → S 1 and S 0 → S 2 absorption regions. The fluorescence excitation spectra of the isolated phenanthrene molecule are compared with the absorption spectra in low temperature matrices. The presence of a 2-type out-of-plane vibrational bands in the S 0 → S 2 absorption spectra indicates that a 1 B 1(πσ*) state lies near the S 2 state. The S 2 → S 1 internal conversion rates at various vibronic levels of S 2 for both compounds have been evaluated from the analysis of profile and width of the individual vibronic bands in the excitation spectra. The excess vibrational energy dependence of the S 2 → S 1 internal conversion rate is the opposite of that shown by the total decay rate in S 1. The excess vibrational energy dependence of the electronic decay rate and the profile of the vibronic absorption bands belonging to the S 0 → S 2 transition are discussed from the viewpoint of the electronic energy gap.