Non-Markovian effects on vibrational energy relaxation in liquids

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Abstract
We consider the non‐Markovian effects on vibrational relaxation which can occur when the bath relaxation rate is comparable to or slower than the relaxation of the vibrational degrees of freedom. We carry out quantum mechanical simulations of a two level system strongly coupled to a bath of known statistical properties (either a Poisson or a Gaussian process) and show that the relaxation is surprisingly insensitive to the nature of the bath. Small oscillations in the relaxation are found for the Poisson simulation which maybe observable in high resolution picosecond experiments. We investigate both cumulant expansion and memory function descriptions of relaxation in the non‐Markovian limit and show that neither approach provides quantitatively accurate results.