Hydrogen bond and residence dynamics of ion–water and water–water pairs in supercritical aqueous ionic solutions: Dependence on ion size and density

Abstract

We have carried out a series of molecular dynamics simulations to investigate the hydrogen bond and residence dynamics of X(-)-water (X=F, Cl, and I) and pairs in aqueous solutions at a temperature of 673 K. The calculations are done at six different water densities ranging from 1.0 to 0.15 g cm(-3). The hydrogen bonds are defined by using a set of configurational criteria with respect to the anion(oxygen)-oxygen and anion(oxygen)-hydrogen distances and the anion(oxygen)-oxygen-hydrogen angle for an anion(water)-water pair. The F(-)-water hydrogen bonds are found to have a longer lifetime than all other hydrogen bonds considered in the present study. The lifetime of Cl(-)-water hydrogen bonds is shorter than that of F(-)-water hydrogen bonds but longer than the lifetime of water-water hydrogen bonds. The lifetimes of I(-)-water and water-water hydrogen bonds are found to be very similar. Generally, the lifetimes of both anion-water and water-water hydrogen bonds are found to be significantly shorter than those found under ambient conditions. In addition to hydrogen bond lifetimes, we have also calculated the residence times and the orientational relaxation times of water molecules in ion(water) hydration shells and have discussed the correlations of these dynamical quantities with the observed dynamics of anion(water)-water hydrogen bonds as functions of the ion size and density of the supercritical solutions.

Water structure near single and multi-layer nanoscopic hydrophobic plates of varying separation and interaction potentials

“…The hydrogen bond distributions of the systems of figures 3 and 4 are shown in figures 5 and 6, respectively. We have used a geometric definition of the hydrogen bonds as was done in earlier studies (Luzar and Chandler 1996a, b;Chowdhury and Pettitt 2005a;Chowdhury and Chandra 2006;Mallik and Chandra 2006). We have, however, used only distance criteria and no angular cut-off was used.…”

Effect of the local hydrogen bonding network on the reorientational and translational dynamics in supercritical water

“…According to literature, the average HB dynamics for pairs i , j of hydrogen bonded molecules could be described using the following time correlation function ͑tcf͒: [46][47][48][49][50][51][52] …”

Structural, single-particle and pair dynamical properties of acetone–chloroform mixtures with dissolved solutes

“…Following previous work [39][40][41][42][43][44][45][46][47][48][49], in order to calculate the dynamics of these hydrogen bond fluctuations, we define two hydrogen bond population variables, h(t) and H(t), where h(t) is unity when a particular acetone-chloroform pair is hydrogen bonded at time t according to the adopted definition and zero otherwise and H(t) = 1 if the acetone-chloroform pair remains continuously hydrogen bonded from t = 0 to time t and it is zero otherwise. To study the breaking dynamics of hydrogen bonds, we calculate the continuous hydrogen bond time correlation function [39][40][41][42][43][44][45][46][47][48][49] S HB (t) = hh(0)H(t)i/hh(0) 2 i which describes the probability that an initially bonded acetone-chloroform pair remains bonded at all times up to t. The associated integrated relaxation time s C HB can be interpreted as the average lifetime of a hydrogen bond between an acetone and a chloroform molecule.…”

“…In this work, we have calculated hydrogen bond relaxation times for both cut-offs. We have used an angular cut-off of 45°for acetone-chloroform hydrogen bond similar to our previous work on hydrogen bonds in aqueous solutions and mixed solvents [42,[45][46][47][48].…”

“…We have used a set of geometric criteria similar to that of used earlier for hydrogen bonds in water [39][40][41][42][43][44][45][46] and binary mixtures [47,48]. A hydrogen bond between an acetone molecule and a chloroform molecule exists if the following distance and angular criteria are satisfied:…”