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.