ON THE EFFECTS OF SOLVENT AND INTERMOLECULAR FLUCTUATIONS IN PROTON-TRANSFER REACTIONS

We present a theory of proton transfer reactions which incorporate the modulation of the proton's potential surface by intermolecular vibrations and the effect of coupling to solvent degrees of freedom. The proton tunnels between states corresponding to it being localized in the wells of a double minimum potential. The resulting tunnel splitting depends on the intermolecular separation. The solvent response to the proton's charge is modeled as that of a damped oscillator, allowing the introduction of friction effects in the solvent dynamics. The rate of transfer is evaluated by perturbation theory in the level splitting. We find that typically the intermolecular and solvent contributions enhance the rate relative to the values obtained in their absence. This effect is evident at low temperature where friction can enhance the rate by increasing opportunity for solvent tunneling. At high temperature the intermolecular motion enhances the rate by sampling over a distribution of tunnel splittings. © 1990 American Institute of Physics.