High temperature aqueous solvent effect on translational and hydrogen bond dynamics of the hydroxyl radical — MD simulation study

Abstract

MD simulations using flexible models were performed to show how velocity autocorrelation functions, diffusion (DOH) and self-diffusion (Dw) coefficients, continuous and intermittent lifetimes of H-donor and H-acceptor bonds depend on: i) transformations in the hydrogen-bond network (HBN) of water below the critical point, and ii) decreasing density at the supercritical isotherm (∼670 K). Contrary to simulations neglecting short-range hydrogen-oxygen interactions, we show that complexation of OHaq with H2O is enhanced by breakage of the continuous HBN, resulting in the increase of OHaq hydrodynamic radius and the DOH values smaller than Dw by 30%. Difference between DOH and Dw increases to 65% at 670 K below the critical density. It is explained by enhanced aggregation of water molecules around OHaq, earlier recognized as the self-trapping mechanism. Except near-ambient conditions, the intermittent lifetime of H-bonds is longer than the translational time, indicating that OHaq is complexed with water and moves as a molecular aggregate.