Empirical Valence Bond Theory Studies of the CH₄ + Cl → CH₃ + HCl Reaction

Abstract

We report a theoretical investigation of the CH4 + Cl hydrogen abstraction reaction in the framework of empirical valence bond (EVB) theory. The main purpose of this study is to benchmark the EVB method against previous experimental and theoretical work. Analytical potential energy surfaces for the reaction have been developed on which quasi-classical trajectory calculations were carried out.The surfaces agree well with ab initio calculations at stationary points along the reaction path and dynamically relevant regions outside the reaction path. The analysis of dynamical data obtained using the EVB method, such as vibrational, rotational and angular distribution functions, shows that this method compares well to both experimental measurements and higher-level theoretical calculations, with the additional benefit of low computational cost.

Computational Study of Competition between Direct Abstraction and Addition–Elimination in the Reaction of Cl Atoms with Propene

“…Internal force-field parameters, such as those for stretch, bend, improper torsional, and torsional motions were determined individually for each diabatic potential using the ab initio data in a manner described previously 18 and are listed in the Supporting Information.…”

“…The H-H van der Waals parameters were taken from the CH4+Cl potential we reported previously and were not altered. 18 In the fits to obtain the EVB2 and EVB3 potentials, all these parameters were kept fixed at the values obtained from the EVB1 fits, and the appropriate coupling terms for the Gaussian functions mentioned above were optimized. In the adopted procedure, we first fitted the CCSD(…”

Dynamical Effects and Product Distributions in Simulated CN + Methane Reactions

“…We have applied this technique to both gas-and liquid-phase reactions previously, showing excellent agreement with experimental results. 12,14,22,30,32 Most of the procedures we use for fitting the CN + CH4 → HCN + CH3 surface have direct analogies to building our Cl + CH4 EVB surface.…”

“…It is the goal of the current work to explore some, but not all, of these ideas in hydrogen abstraction from hydrocarbons by CN. In so doing, we build on our recent quantum-state-resolved dynamics measurements and simulations of halogen-atom reactions with saturated 12 and unsaturated polyatomic reactants in gas [13][14] and liquid phases. [15][16][17] A lag exists in our understanding of the gas-phase CN hydrogen-abstraction dynamics relative to those in the condensed phase.…”

“…36 The initial parameters come from the CH4 + Cl potential, 12 adopting C values for N. The fitted parameters and the functional form, which is sufficiently flexible without introducing over-fitting to the ab initio points, are given in the Supporting Information.…”