Kinetic and H-atom product study of the C + C6H6 reaction at low temperatures

Abstract

The reactions of atomic carbon in its ground electronic state configuration, C(3P), are potentially important processes in astrochemistry due to the large abundance of C(3P) atoms in the interstellar medium (ISM) and its high overall reactivity towards a wide range of molecules. Although benzene, C6H6, has not been detected in the dense ISM, its presence at high abundance levels is inferred through the detection of functionalized derivatives. Here we present a combined experimental and astrochemical modeling investigation of the gas-phase C(3P) + C6H6 reaction. Experimentally, rate constants were determined over the 50-296 K range using the Laval nozzle technique coupled with pulsed laser photolysis and laser induced fluorescence for C(3P) generation and detection respectively. Product yields of atomic hydrogen, H(2S) were also measured at 177 and 296 K to provide some information on the product channels of the reaction. The measured rate constants are very large, between 3.3 and 5.7 x 10-10 cm3 s-1 indicating the fast, barrierless nature of the reaction, while the H-atom yields are all below 10 % when compared to the C(3P) + C2H4 reference reaction. As the C(3P) + C6H6 reaction is not currently included in astrochemical databases, its influence on the simulated abundances of C6H6 and related species was tested using a gas-grain model of dense interstellar clouds. The C(3P) + C6H6 reaction is shown to be the main loss process for interstellar benzene, while different hypotheses regarding the product channels are discussed in the context of observations to shed light on the preferred formation pathways.