Kinetics of C2(a3Πu) radical reactions with alkanes by LIF

The reactions of C2(a3Πu) radicals with a series of alkanes have been studied at room temperature and 6.5 torr total pressure using the pulsed laser photolysis/laser-induced fluorescence technique. C2(a3Πu) radicals were generated by photolysis of C2Cl4 with the focused output from the fourth harmonic of a Nd: YAG laser at 266 nm. The relative concentration of C2(a3Πu) radicals was monitored on the (0,0) band of the C2(d3Πg←a3Πu) transition at 516.5 nm by laser-induced fluorescence. From the analysis of the relative concentration-time behavior of C2(a3Πu) under pseudofirst-order conditions, the rate constants for the reactions of C2(a3Πu) with alkanes (C1–C8) were determined. The rate constant increases linearly with the increasing of the number of CH2 groups in the alkanes. The experimental results indicate that the reaction of C2(a3Πu) with small alkanes (C1–C8) follows the typical hydrogen abstraction process. Based on the correlation of the experimental results with the bond dissociation energy of the alkanes, the reactions of C2(a3Πu) with small alkanes likely proceed via the mechanism of hydrogen abstraction.