Angular momentum dependent friction slows down rotational relaxation under non-equilibrium conditions

TL;DR

This paper investigates how angular momentum-dependent friction influences the slow-down of rotational relaxation in non-equilibrium conditions, revealing that traditional models need to incorporate angular momentum effects for accuracy.

Contribution

The authors develop a generalized Fokker-Planck equation with angular momentum-dependent friction, improving the modeling of rotational relaxation far from equilibrium.

Findings

Rotational friction depends algebraically on angular momentum.

Calculated correlation functions match molecular dynamics simulations.

Angular momentum dependence is crucial for accurate non-equilibrium relaxation modeling.

Abstract

It has recently been shown that relaxation of the rotational energy of hot non-equlibrium photofragments (i) slows down significantly with the increase of their initial rotational temperature and (ii) differs dramatically from the relaxation of the equilibrium rotational energy correlation function, manifesting thereby breakdown of the linear response description [Science 311, 1907 (2006)]. We demonstrate that this phenomenon may be caused by the angular momentum dependence of rotational friction. We have developed the generalized Fokker-Planck equation whose rotational friction depends upon angular momentum algebraically. The calculated rotational correlation functions correspond well to their counterparts obtained via molecular dynamics simulations in a broad range of initial non-equilibrium conditions. It is suggested that the angular momentum dependence of friction should be taken into account while describing rotational relaxation far from equilibrium.