Water as a Lévy Rotor.

Area of Science:

• Physical Chemistry
• Chemical Physics
• Molecular Dynamics

Background:

• Understanding molecular rotational dynamics is crucial for chemical processes.
• Anomalous diffusion deviates from classical Brownian motion.
• Nuclear Magnetic Resonance (NMR) relaxation provides insights into molecular dynamics.

Purpose of the Study:

• To derive and validate a Lévy rotor model for intramolecular vector dynamics in water.
• To investigate the transition from Brownian to anomalous rotational dynamics in water.
• To quantify the intramolecular contribution to the longitudinal NMR relaxation rate in water.

Main Methods:

• Derivation of a probability density function for angular evolution using the Lévy rotor model.
• Molecular dynamics simulations of water at 298 K.
• Estimation of intramolecular contribution to longitudinal NMR relaxation rate (R_{1,intra}).

Main Results:

• The Lévy rotor model accurately describes intramolecular ^{1}H─^{1}H dynamics in water.
• Water's rotational dynamics exhibit a transition from Brownian to anomalous behavior due to hydrogen bond dynamics.
• The intramolecular contribution (R_{1,intra}) accounts for 65%±7% of the total relaxation rate at room temperature.

Conclusions:

• The Lévy rotor model provides a robust framework for studying anomalous molecular dynamics.
• Hydrogen bond dynamics significantly influence the rotational dynamics of water.
• Intramolecular interactions play a dominant role in the NMR relaxation of water at room temperature.