EXCITED STATE AND VIBRATIONAL GROUND STATE STUDIES OF CAROTENES AND CHLOROPHYLL MONOMERS AND DIMERS
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Date
1983
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Publisher
Ohio State University
Abstract
Using a nanosecond tunable pulsed laser we have obtained the vibrational Raman spectrum of short lived excited states of all trans $\beta$-carotene and dimers of dry Chlorophyll a in hexane. The position of Raman shifts of the $S_{1}$ states of all trans $\beta$-carotene which has a lifetime 265fs, is determined by applying the technique of time resolved Raman spectroscopy and our data suggest that only small differences exist in the frequencies of corresponding modes of $S_{1}$ and the $S_{0}$ ground state. A high resolution study of the Raman excitation profile of a normal mode of trans $\beta$-carotene suggest the presence of another electronic state and Raman spectrum from this state too was recorded. Excited level Raman spectroscopic studies were also made of a solution of dry Chl a in hexane, where the majority species is the Chl a dimer. We report the first observation of hole burning in the Raman excitation profile of normal modes in the ground state from the dimer. This phenomenon is explained in terms of ground state bleaching and the occurrence of Raman scattering from exciton levels of the dimer at $14800 cm^{-1}$ and $16300 cm^{-1}$.
Description
$^{*}$Department of Chemistry, Carleton Universtiy, Ottawa K1S 586, Ont, Canada.
Author Institution: Department of Chemistry Carleton, University Ottawa
Author Institution: Department of Chemistry Carleton, University Ottawa