We have observed the polarization resolved two-photon fluorescence excitation spectra of jet cooled (2 to 8 K) indole. ¹L_a lines are distinguished from ¹L_b lines by their reduced intensity under excitation with circularly polarized light and by their sharp Q branch using linear polarization. Extensive one-photon excitation spectra of complexes of indole with methanol, H₂O, and D₂O have been obtained. The pair of '¹L_a' lines at 455 and 480 cm^-1 shift only a few wavenumbers more than the ¹L_b lines in the type I complexes (where indole is thought to be a H-bond donor) but undergo large intensity redistribution, casting doubt on their assignment as the ¹L_a 'origin'. In the methanol complex I, the 480 cm^-1 line does retain its ¹L_a character (as the origin at -160 cm^-1 from the bare origin also retains all of its ¹L_b character). Previous work on the D₂O complex revealed that the Franck-Condon active intermolecular vibrations involve translation of the water center-of-mass by 0.4 angstroms in the case of the type II ('(pi) ') complex at -450 cm^-1. Except for a few transitions in the complex indole + methanol, type II peaks are not seen at higher energies in the spectra of the complexes due to their low intensity.

Date Published: 17 August 1994
PDF: 10 pages
Proc. SPIE 2137, Time-Resolved Laser Spectroscopy in Biochemistry IV, (17 August 1994); doi: 10.1117/12.182736

Published in SPIE Proceedings Vol. 2137:
Time-Resolved Laser Spectroscopy in Biochemistry IV
Joseph R. Lakowicz, Editor(s)