Water as a Le acute accent vy Rotor

A probability density function describing the angular evolution of a fixed-length atom-atom vector as a Le ' vy rotor is derived containing just two dynamical parameters: the Le ' vy parameter alpha and a rotational time constant tau. A Le ' vy parameter alpha < 2 signals anomalous (non-Brownian) motion. Molecular dynamics simulation of water at 298 K validates the probability density function for the intramolecular 1H-1H dynamics. The rotational dynamics of water is found to be approximately Brownian at subpicosecond time intervals, becomes increasingly anomalous at longer time intervals due to hydrogen-bond breaking and reforming, before becoming indistinguishable from Brownian dynamics beyond about 25 ps. The Le ' vy rotor model is used to estimate the intramolecular contribution to the longitudinal nuclear-magneticresonance (NMR) relaxation rate R1,intra. It is found that R1,intra contributes 65% 17% to the overall relaxation rate of water at room temperature.

Automated summary

A probability density function describing the angular evolution of a fixed-length atom-atom vector as a Le 'vy rotor is derived with the Levy parameter alpha and a rotational time constant tau. Molecular dynamics simulation of water validates the function for intramolecular 1H-1H dynamics, showing that water's rotational dynamics are approximately Brownian at short time intervals and become increasingly anomalous at longer intervals due to hydrogen-bond breaking. The Levy rotor model estimates that intramolecular contribution to the longitudinal NMR relaxation rate R1,intra accounts for 65% 17% of water's overall relaxation rate at room temperature.