17 August 1994 1La transitions of jet-cooled indoles and complexes from two-photon fluorescence excitation
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We have observed the polarization resolved two-photon fluorescence excitation spectra of jet cooled (2 to 8 K) indole. 1La lines are distinguished from 1Lb 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 '1La' lines at 455 and 480 cm-1 shift only a few wavenumbers more than the 1Lb 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 1La 'origin'. In the methanol complex I, the 480 cm-1 line does retain its 1La character (as the origin at -160 cm-1 from the bare origin also retains all of its 1Lb 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.
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Pedro L. Muino, Pedro L. Muino, Patrik R. Callis, Patrik R. Callis, } "1La transitions of jet-cooled indoles and complexes from two-photon fluorescence excitation", Proc. SPIE 2137, Time-Resolved Laser Spectroscopy in Biochemistry IV, (17 August 1994); doi: 10.1117/12.182736; https://doi.org/10.1117/12.182736


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