Solvent nuclear quantum effects in electron transfer reactions. II. Molecular dynamics study on methanol solution

Solvent nuclear quantum effects in outer-sphere electron transfer (ET) reactions in methanol solution are examined via a molecular dynamics simulation analysis. The energy gap law of the quantum mechanical ET rate constant is decomposed into contributions from solvent intramolecular vibrations and other low-frequency intermolecular (collective) modes. It is shown that the high-frequency stretching and bending vibrations from the hydroxyl part of the solvent methanol exhibit marked quantum effects on the ET rate despite of their fractional contributions to the reorganization energy (computed to be <4%). A scaling property of the quantum energy gap law is proposed, which would be useful to coordinate data from variety of donor-acceptor systems where the solvent spectral density may have similar profile but the other parameters such as the reaction distance and the reorganization energy may vary. The results are compared with our previous study on aqueous ETs [K. Ando, J. Chem. Phys. 106, 116 (1997)]. (C) 2001 American Institute of Physics.