Site selective photoselection study of indole in argon matrix: location of the 1L a origin

Abstract

Polarized fluorescence excitation and dispersed fluorescence spectra of indole in solid Ar at 20 K under site selective conditions have revealed that ν 28 is Herzberg-Teller (HT) active, both in the excitation and the fluorescence spectrum. The two lines 455 and 480 cm −1 above the 1L b origin are a Fermi doublet involving 28 0 1 and the out-of-plane combination 39 0 141 0 1 and derive 1L a optical character via the HT coupling by ν 28. The true 1L a origin appears to be about 1400 cm −1 above the 1L b origin in vapor, as discerned by the differential red shift in the Ar matrix.