Angular momentum dependent friction slows down rotational relaxation under nonequilibrium conditions

Area of Science:

• Chemical Physics
• Physical Chemistry
• Molecular Dynamics

Background:

• Recent studies show rotational energy relaxation in hot photofragments is temperature-dependent and deviates from equilibrium descriptions.
• This deviation indicates a breakdown in linear response theory for describing these systems.

Purpose of the Study:

• To investigate the cause of the anomalous rotational energy relaxation observed in hot nonequilibrium photofragments.
• To develop a theoretical model that accounts for the observed deviations from linear response theory.

Main Methods:

• Development of a generalized Fokker-Planck equation incorporating angular momentum-dependent rotational friction.
• Comparison of theoretical calculations with molecular dynamics simulations.

Main Results:

• The developed generalized Fokker-Planck equation accurately reproduces rotational correlation functions from molecular dynamics simulations.
• The model demonstrates that angular momentum dependence of rotational friction explains the observed nonequilibrium relaxation behavior.

Conclusions:

• The angular momentum dependence of rotational friction is crucial for accurately describing rotational relaxation far from equilibrium.
• Linear response theory is insufficient for hot nonequilibrium photofragments; friction's angular momentum dependence must be considered.