Fluorescence excitation spectra of indole, 3-methyl indole, and 3-indole acetic acid in supersonic jets

Abstract

In this paper we report on the laser-induced fluorescence spectra of indole, 3-methyl indole, and 3-indole acetic acid in pulsed supersonic expansions of He. The electronic origin of the first excited (1Lb) state is 35 233 cm−1 for indole, 34 887 cm−1 for 3-methyl indole, and 34 044 cm−1 for 3-indole acetic acid. On the basis of the energetics and fluorescence lifetimes, the spectral features at excess vibrational energies EV=0–2200 cm−1 for indole and EV=0–1600 cm−1 for 3-methyl indole were assigned to the vibrational level structure within a single electronic manifold. The second electronically excited (1La) state is not located in the above energy ranges. The energetics of selective solvation of 3-methyl indole was inferred from the spectra of the van der Waals complexes with Ar, H2O, and D2O, which provide information on microscopic solvent shifts of the electronic origin and of some prominent vibrational excitations of the 1Lb states.