Kinetic isotope effects for nonadiabatic proton transfer reactions in a polar environment. 2. Comparison with an electronically diabatic description

Kinetic isotope effects (KIEs) for proton transfer (PT) in a polar environment in the nonadiabatic, i.e., tunneling, regime was presented in the preceding paper (Kiefer, P. M.; Hynes, J. T, J. Phys. Chem. A 2004, 108, 0000). The present paper extends this work by comparing the electronically adiabatic (EAd) view of tunneling PT reactions of that paper with electronically diabatic (EDi) tunneling PT descriptions. Compared to the EAd PT description, the electronically diabatic character inherent in EDi PT produces smaller rate constants, larger KIE magnitudes with a smaller variation with reaction asymmetry, and a smaller activation energy difference E-AD - E-AH. Specifically, the EDi PT picture is characterized by a "nonadiabatic coupling" element that is smaller and less sensitive to both H-bond motion and proton vibrational excitation than those for EAd PT.