The role of potential energy surface in quantum mechanical tunneling: A computational perspective

Abstract

The contribution of the nature of potential energy surface (PES) on quantum mechanical tunneling have been investigated for a series of hydrogen atom transfer (HAT) reactions at state-of-the-art composite CBS-QB3 and modified G4MP2 method. Two series of HAT reactions have been considered to get different kinds of PES e.g., (i) HAT from different substrate by same radical abstractor and (ii) HAT from same substrate by different radical abstractor. It has been found that approximately more than 90% of the overall reactions have been proceeds through tunneling path even at room temperature (298 K) for all the investigated reactions. The symmetric i.e., thermo-neutral PES possesses more tunneling than the asymmetric i.e., exothermic or endothermic PES. It is due to the higher degree of overlap between reactant and product wave-function in symmetric PES which facilitates to cross the barrier through tunnel. Both CBS-QB3 and G4MP2 results provides similar kind of trend.