HOMOGENEOUS LINE-WIDTH OF THE DIFFERENT VIBRONIC BANDS OF RETINAL ABSORPTION IN BACTERIORHODOPSIN BY THE HOLE-BURNING TECHNIQUE

Using the hole-burning technique, resolved vibrational structure was o bserved in the retinal absorption spectrum of bacteriorhodopsin (bR) i n poly(vinyl alcohol) (PVA) film at 10 K with 556 and 632 nm irradiati on. The homogeneous line widths of v = 1 and v = 2 vibronic bands are estimated from the deconvolution of the observed spectrum. The absorpt ion maximum is found to shift by 100-200 cm(-1) by using the two excit ation wavelengths; resulting from partial site selection due to the co ntribution of inhomogeneous broadening. The hole width produced by exc itation near the zero-phonon band is found to be similar to 1250 cm(-1 ), which corresponds to a homogeneous width of similar to 600 cm(-1), and the low limit of dephasing time can be estimated as 20 fs. This wi dth is found to be independent of the vibronic band observed.