Ranjit Biswas

Ionic mobility in alcohols: From dielectric friction to the solvent–berg model

A self-consistent microscopic theory is used to calculate the mobility of rigid univalent ions in methanol, ethanol, and propanol at room temperature. The theoretical predictions are in good agreement with the long-known experimental results. In particular, the theory reproduces the nonmonotonic size dependence of the limiting ionic conductance accurately. The relation between the polar solvation dynamics of an ion and its mobility is clarified. The theory also explains how a dynamical version of the classical solvent–berg model can be recovered for small ions in the limit of slow liquids.

Vibrational energy relaxation, nonpolar solvation dynamics and instantaneous normal modes: Role of binary interaction in the ultrafast response of a dense liquid

Recently instantaneous normal mode analysis has revealed an interesting similarity of the solvent dynamical influence on two rather different phenomena, namely vibrational energy relaxation (VER) and nonpolar solvation dynamics (NPSD). In this work we show that this similarity can be rationalized from a mode coupling theoretic analysis of the dynamic response of a dense liquid. The present analysis demonstrates that VER and the initial NPSD are coupled primarily to the binary part of the frequency dependent frictional response of the liquid. It is found that for strong solute–solvent interaction, the initial decay of nonpolar solvation dynamics can proceed with time constant less than 100 fs. In addition, a very good agreement between the calculated and the simulated VER rates have been obtained for a large range of frequency.

Activated barrier crossing dynamics in slow, viscous liquids

Experimental studies of reaction rates in slow, viscous liquids have often led to results at variance with conventional theoretical approaches. Here we present a self-consistent microscopic calculation of the rate which uses for the first time, the mode coupling theory (MCT) to obtain the frequency dependent friction. When this microscopic expression for the friction is used to obtain the barrier crossing rate from the Grote–Hynes (G–H) formula, the following results are found. At intermediate viscosities, the calculated rate exhibits a fractional viscosity dependence with parameter values in agreement with the experimental results. For example, we find an exponent equal to 0.8 when the barrier frequency

Isomerization dynamics in viscous liquids: Microscopic investigation of the coupling and decoupling of the rate to and from solvent viscosity and dependence on the intermolecular potential

(omega_b)

ION SOLVATION DYNAMICS IN SUPERCRITICAL WATER

is equal to

Comment on “Dynamics of solvated ion in polar liquids: An interaction-site-model description” [J. Chem. Phys. 108, 7339 (1998)]

2times10^{13}s^{-1}

Anomalous solubility of organic solutes in supercritical water: A molecular explanation

, whereas the earlier calculations obtained an unrealistic value close to (0.1) for this value of the barrier frequency. At very high viscosities we find an inverse logarithmic dependence of the rate on viscosity. This prediction can be tested against experiments.

SOLVATION DYNAMICS OF A CHARGE BUBBLE IN WATER

A detailed investigation of viscosity dependence of the isomerization rate is carried out for continuous potentials by using a fully microscopic, self-consistent mode-coupling theory calculation of both the friction on the reactant and the viscosity of the medium. In this calculation we avoid approximating the short time response by the Enskog limit, which overestimates the friction at high frequencies. The isomerization rate is obtained by using the Grote–Hynes formula. The viscosity dependence of the rate has been investigated for a large number of thermodynamic state points. Since the activated barrier crossing dynamics probes the high-frequency frictional response of the liquid, the barrier crossing rate is found to be sensitive to the nature of the reactant–solvent interaction potential. When the solute–solvent interaction is modeled by a 6–12 Lennard-Jones potential, we find that over a large variation of viscosity (η), the rate (k) can indeed be fitted very well to a fractional viscosity dependence...

Polar and Nonpolar Solvation Dynamics, Ion Diffusion, and Vibrational Relaxation: Role of Biphasic Solvent Response in Chemical Dynamics

A theoretical study of ionic solvation dynamics in supercritical water is presented. The short-time decay of the calculated equilibrium solvation energy time correlation function

Anomalous ion diffusion in dense dipolar liquids.

(S_E(t))