Quantum effects on the solvent contribution to the activation free energy

Quantum effects on the activation free energy for the transfer of a quantum particle between two ions immersed in a classical dipolar solvent are investigated. The bare potential for the quantum particle-ion complex has an intrinsic barrier that is negligible compared to k(B)T and corresponds to a strongly hydrogen bonded system if the quantum particle is a proton. In this circumstance the activation free energy is dominated by solvent contributions. We compare the solvent free energies along the reaction coordinate for a classical particle with charge +1, a proton and a muon. The quantum calculations are carried out using Feynman's path integral methods. The smaller mass of the muon gives rise to enhanced quantum effects and allows one to probe the effects of the dispersion of the charge density of the particle undergoing transfer on the solvent contribution to the free energy.