Rate Constant for the Reaction C sub(2)H sub(5) + HBr arrow right C sub(2)H sub(6) + Br

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 2012-06, Vol.116 (24), p.5847-5855-5847-5855
• Main Authors: Golden, David M, Peng, Jingping, Goumri, A, Yuan, J, Marshall, Paul
• Format: Article
• Language: English
• Subjects: Activation energy; Adducts; Anharmonicity; Dissociation energy; Energy of dissociation; Indication; Rate constants; Reaction kinetics
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp209081v

RRKM theory has been employed to analyze the kinetics of the title reaction, in particular, the once-controversial negative activation energy. Stationary points along the reaction coordinate were characterized with coupled cluster theory combined with basis set extrapolation to the complete basis set limit. A shallow minimum, bound by 9.7 kJ mol super(-1) relative to C sub(2)H sub(5) + HBr, was located, with a very small energy barrier to dissociation to Br + C sub(2)H sub(6). The transition state is tight compared to the adduct. The influence of vibrational anharmonicity on the kinetics and thermochemistry of the title reaction were explored quantitatively. With adjustment of the adduct binding energy by 4 kJ mol super(-1), the computed rate constants may be brought into agreement with most experimental data in the literature, including new room-temperature results described here. There are indications that at temperatures above those studied experimentally, the activation energy may switch from negative to positive.