Translation-Rotation Coupling in the Dynamics of Linear Molecules in Water

TL;DR

This study uses computer simulations to analyze how the rotational and translational motions of linear molecules like CO, NO, and CN- in water are interconnected, revealing limitations of hydrodynamic models and proposing a mode coupling theory for better understanding.

Contribution

The paper introduces a mode coupling theory approach to better explain the complex translation-rotation coupling in linear molecules within water, surpassing hydrodynamic predictions.

Findings

Translational diffusion is strongly coupled to rotational dynamics.

Hydrodynamic predictions are largely insufficient for rotational diffusion.

Mode coupling theory provides a better understanding of the dynamics.

Abstract

We study by computer simulations the coupled rotational and translational dynamics of three important linear diatomic molecules, namely, carbon monoxide (CO), nitric oxide (NO) and cyanide ion (CN-) in water. Translational diffusion of these molecules is found to be strongly coupled to their own rotational dynamics which in turn are coupled to similar motions of surrounding water. We examined the validity of hydrodynamic predictions and found them to be largely insufficient, particularly for rotational diffusion. A mode coupling theory approach is developed and applied to understand the complexity of translation-rotation coupling.