Effect of nonequilibrium solvation on chemical reaction rates. Variational transition-state-theory studies of the microsolvated reaction Cl-(H2O)n + CH3Cl

The authors present a potential energy surface for the microhydrated S{sub N}2 reaction of a chloride ion with methyl chloride in the presence of one or two water molecules. All degrees of freedom are included. The authors analyze the stationary points corresponding to reactant, ion-dipole complex, and transition state for the monohydrated and the dihydrated reactions, and they use generalized transition-state theory to evaluate the rate constants for these reactions. A noteworthy feature of the dynamics calculations is that vibrational zero point effects are included, as are effects of quantization on vibrational heat capacities and entropies, and water molecules are treated as nonrigid. The authors find that the rate constant at 300 K decreases from the gas-phase value of 3.5 {times} 10{sup {minus}14} cm{sup 3} molecule {sup {minus}1} s{sup {minus}1} to a value of 1.1 {times} 10{sup {minus}17} cm{sup 3} molecule{sup {minus}1} s{sup {minus}1} for the monohydrated reaction and to a value of 3.7 {times} 10{sup {minus}20} cm{sup 3} molecule{sup {minus}1} s{sup {minus}1} for the dihydrated reaction.