The Use of Resonant Light Scattering as a Probe of Picosecond and Subpicosecond Relaxation and Dephasing Times in the Excited State

Abstract

Most biological macromolecules exhibit optical absorption lineshapes that are spectrally broad even at liquid He temperatures. Because line broadening mechanism might originate from relaxation and dephasing processes that are of biological and physical importance, it is of interest to deconvolute the various mechanisms that are contributing to a given spectrally broadened optical transition. When the line broadening is caused by relaxation and dephasing processes that are occurring on a sub-picosecond timescale it is no longer routinely feasible to apply the elegant time resolved non-linear techniques in the determination of the dephasing and relaxation rates. Instead, these rates and mechanisms are more effectively determined by monitoring the spectrum of resonant scattered monochromatic light [1]. In this paper it will be shown that resonant light scattering can be used to expose the relaxation and dephasing origin of line broadening in the visible absorption spectrum of ferrocyto-chrome c at room temperature and at liquid He temperatures.