Fluorescence Spectra of Phenanthridine Isolated in the Supersonic Jet Expansion

Following the analysis of laser induced fluorescence spectrum of 7,8-benzoquinoline molecule, observed under conditions of isolation in the supersonic jet expansion, the ab initio analysis of laser induced fluorescence spectrum of phenanthridine, observed under the same experimental condi-tions, was performed. This analysis included: optimization of equilibrium geometry of phenanthridine in its first excited S1 singlet state and computa-tions of the frequencies of vibrational fundamental modes together with their geometry changes between the excited and the ground state. Comparison of the results of calculations with experimental data revealed their good agree-ment and an increase in the vibrational activity in the fluorescence spectrum in comparison to fluorescence spectrum of phenanthrene molecule (which is a parent aromatic hydrocarbon of phenanthridine and of 7,8-benzoquinoline). Such an increase in vibrational activity in the fluorescence spectrum was ear-lier observed also for 7,8-benzoquinoline molecule. Present analysis shows that this effect is due to molecular symmetry reduction caused by the sub-stitution of nitrogen atom into the aromatic rings system of phenanthrene, as well as to the changes of equilibrium structure between the ground and excited states. PACS numbers: 82.20.Wt, 31.15.Ar, 33.20.Tp 1