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

Graphical abstract Highlights • Self-diffusion (D w) and D OH coefficients comparable up to 470 K. • Above 470 K D OH by 30% lower due to enhanced complexation of OH with H 2 O. • Continuous lifetime ∼10−14 s calculated for both H-donor and H-acceptor bond. • Intermittent lifetime 4 ps (373 K) drops to 1 ps (673 K) exceeding translational time. • Conclusions on OH aq translational dynamics depend on model potential used. Abstract MD simulations using flexible models were performed to show how velocity autocorrelation functions, diffusion (D OH) and self-diffusion (D w) 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 OH aq with H 2 O is enhanced by breakage of the continuous HBN, resulting in the increase of OH aq hydrodynamic radius and the D OH values smaller than D w by 30%. Difference between D OH and D w increases to 65% at 670 K below the critical density. It is explained by enhanced aggregation of water molecules around OH aq , 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 OH aq is complexed with water and moves as a molecular aggregate. [ABSTRACT FROM AUTHOR]