Molecular reorientation in hydrogen-bonding liquids: through algebraic $\sim t^{-3/2}$ relaxation toward exponential decay

TL;DR

This paper introduces a model for orientational relaxation in hydrogen-bonding liquids, revealing algebraic and exponential decay behaviors influenced by dissipation and memory effects, and applies it to interpret experimental and simulation data.

Contribution

The model uniquely combines algebraic and exponential relaxation components, incorporating memory effects and dissipation parameters for hydrogen-bonding liquids.

Findings

Librational relaxation exhibits a t^{-3/2} algebraic decay.

Long-time relaxation is exponential and governed by rotational energy dissipation.

The model successfully interprets molecular dynamics and pump-probe experimental data.

Abstract

We present a model for the description of orientational relaxation in hydrogen-bonding liquids. The model contains two relaxation parameters which regulate the intensity and efficiency of dissipation, as well as the memory function which is responsible for the short-time relaxation effects. It is shown that the librational portion of the orientational relaxation is described by an algebraic $\sim t^{-3/2}$ contribution, on top of which more rapid and non-monotonous decays caused by the memory effects are superimposed. The long-time behavior of the orientational relaxation is exponential, although non-diffusional. It is governed by the rotational energy relaxation. We apply the model to interpret recent molecular dynamic simulations and polarization pump-probe experiments on $HOD$ in liquid $D_{2}O$ [C. J. Fecko et al, J. Chem. Phys. 122, 054506 (2005)].