Abstract

Quantum mechanical tunnelling of atoms is emerging as an ubiquitous phenomenon in chemistry. Every chemical reaction that includes a hydrogen transfer can be expected to be influenced by tunnelling at room temperature. While simulations can monitor tunnelling directly, experimental approaches can only detect the consequences. We use instanton theory, based on statistical Feynman path integrals, to find the most probable tunnelling path and the reaction rate. This is used to investigate the formation of H2 on the surface of carbonaceous dust grains in space [1] as well as the deuteration of interstellar methanol [2]. Large kinetic isotope effects in this and other reactions can be explained by the tunnelling contribution.

Tunnelling paths are also calculated for the decay of substituted singlet carbenes [3] for which the different lengths of the tunnelling paths distinguish the probability of two reaction channels [4]. Finally, we applied the method to estimate the amount of tunnelling in an enzymatic system in a QM/MM description, glutamate mutase [5].

1. T.P.M. Goumans, J. Kästner, Angew. Chem. Int. Ed. 49 (2010) 7350
2. T.P.M. Goumans, J. Kästner, J. Phys. Chem. A 115 (2011) 10767
3. J. Kästner, Chem. Eur. J. 19 (2013) 8207
4. P.R. Schreiner, H.P. Reisenauer, D. Ley, D. Gerbig, C.H. Wu, W.D. Allen, Science 332 (2011), 1300
5. J.B. Rommel, J. Kästner, J. Am. Chem. Soc. 133 (2011), 10195