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

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.