Low-temperature zero phonon lineshapes with various Brownian oscillator spectral densities

Abstract

The Brownian oscillator model has been successfully employed for modeling solvation dynamics in numerous femtosecond measurements. To a very large extent, this work has been interpreted on the basis of high-temperature limits of the theory. We present an analysis of the low temperature limit, which is particularly important for hole burning, photon echo, and single molecule spectroscopic experiments. Several forms for the bath spectral density are employed to compute zero phonon absorption line shapes. We show that in all cases the zero phonon linewidth vanishes at low temperatures, and that the line becomes asymmetric with a sharp rise at the red edge, as expected qualitatively.