Dynamics of linear molecules in water: Translation-rotation coupling in jump motion driven diffusion

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Molecular Dynamics

Background:

• Understanding molecular motion in solution is crucial for chemical reactions and material properties.
• Previous studies often treated translational and rotational dynamics independently.
• Hydrodynamic theories provide a framework but may oversimplify complex molecular interactions.

Purpose of the Study:

• To investigate the coupled translational and rotational dynamics of diatomic molecules (CO, NO, CN-) in water.
• To explore the interplay between solute molecular motion and solvent dynamics.
• To evaluate the accuracy of hydrodynamic predictions for these coupled motions.

Main Methods:

• Extensive computer simulations using molecular dynamics.
• Theoretical analysis employing a mode coupling theory approach.
• Comparison of simulation results with experimental diffusion coefficients.

Main Results:

• Translational diffusion is strongly coupled to rotational dynamics for CO, NO, and CN- in water.
• Coupled orientational jump motions are significant for all studied molecules.
• Hydrodynamic predictions were found to be inadequate, especially for rotational diffusion.
• CN- exhibits distinct dynamics compared to CO and NO.

Conclusions:

• Molecular dynamics simulations and mode coupling theory offer insights into complex translation-rotation coupling.
• The findings highlight the limitations of simplified hydrodynamic models in describing molecular motion in liquids.
• Accurate modeling of these coupled dynamics is essential for predicting molecular behavior in solution.