Ab Initio Investigation of Ethane Dissociation Using Generalized Transition State Theory

The simple carbon-carbon scission of ethane is investigated by performing quantum mechanical calculations. The approach described in this paper was developed to determine dissociation rate constants for both small and large organic molecules, such as n-alkanes or alkyl-benzenes, for reasonable ranges of computation time and accuracy. The methodology that we propose is based on generalized transition state theory, where transition states are defined along rate constant profiles and not along potential energy curves. Simulations reported in this paper aim to validate this methodology by examining the dissociation of ethane. Calculations, performed at the DFT B3:LYP 6-31G** theory level, correctly account for the looseness of the transition state as a function of temperature. Dissociation activation parameters obtained by this method are in good agreement with data available in the literature. Despite the assumptions made, the order of magnitude and the specific temperature dependence of rate constants for methyl recombination are also fairly predicted.