Kinetics of thermal excitation of a molecule in a condensed medium

TL;DR

This paper develops a microscopic model for the thermal excitation of a molecule's vibrational ground state in a condensed medium, deriving a master equation and analyzing the temperature dependence of the excitation rate.

Contribution

It introduces a new microscopic model and provides an analytical expression for the rate constant of molecular thermal excitation in condensed media.

Findings

Rate constant is temperature-independent at low temperatures.

Rate constant increases linearly with temperature at high temperatures.

Derived a master equation governing vibrational level occupancies.

Abstract

A microscopic model for thermal excitation of vibrational ground state of a molecule interacting with a condensed medium is developed. The master equation for evolution of occupancies of the vibrational levels is derived. The rate constant limiting the process of molecular thermal excitation is determined analytically. It is shown that while this quantity is independent of temperature at low temperatures coinciding with a rate speed limit for quantum transitions due to uncertainty principle, at high temperatures it rather linearly rises with temperature according to the Einstein's relation for adiabatic transitions.