Semiclassical evaluation of kinetic isotope effects in 13-atomic system.

The semiclassical instanton approach discussed by Kryvohuz [J. Chem. Phys. 134, 114103 (2011)] is applied to calculate kinetic H/D isotope effect (KIE) of intramolecular hydrogen transfer in cis-1,3-pentadiene. All 33 vibrational degrees of freedom are treated quantum mechanically with semiclassical approximation. Nuclear quantum effects such as tunneling under the barrier and zero-point energy are automatically incorporated in the theory, and are shown to be responsible for the observed appreciable kinetic isotope effect in cis-1,3-pentadiene. Over the barrier passage is also automatically included. Numerical calculations are performed on an empirical valence bond potential energy surface and compared with the previous experimental and theoretical studies. An estimation of heavy-atom (12)C/(13)C KIE in the same system is also provided and the factors contributing to it are discussed.