Non-Markovian optical dephasing dynamics in room temperature liquids investigated by femtosecond transient absorption spectroscopy: Theory and experiment

Abstract

This paper examines the electronic dephasing dynamics of the dye molecule HITCI in an ethylene glycol solution. Degenerate transient absorption data are presented as a function of laser pulse width and detuning from the absorption maximum. The dephasing dynamics revealed by the experimental results are shown to be non-Markovian. The experimental data cannot be quantitatively described by stochastic theories that assume a single relaxation time for the solvent. A model is presented that includes contributions from both fast and slow modulations to the absorption line shape. Using this approach, quantitative agreement is observed between theory and experiment. These results clearly indicate that multiple time scales for liquid dynamics contribute to the absorption line shape of solute molecules. The solvent parameters obtained are discussed in light of results from complementary experiments designed to measure characteristic relaxation times.