Kinetic and Product Study of the Reactions of C(1D) with CH4 and C2H6 at Low Temperature

The reactions of atomic carbon in its first excited 1 D state with both CH 4 and C 2 H 6 have been investigated using a continuous supersonic flow reactor over the 50-296 K temperature range. C( 1 D) atoms were generated in situ by the pulsed laser photolysis of CBr 4 at 266 nm. To follow the reaction kinetics, product H atoms were detected by vacuum ultraviolet laser-induced fluorescence at 121.567 nm. Absolute H-atom yields for both reactions were determined by comparison with the H-atom signal generated by the reference C( 1 D) + H 2 reaction. Although the rate constant for the C( 1 D) + CH 4 reaction is in excellent agreement with earlier work at room temperature, this process displays a surprising reactivity increase below 100 K. In contrast, the reactivity of the C( 1 D) + C 2 H 6 system decreases as the temperature falls, obeying a capture-type rate law. The H-atom product yields of the C( 1 D) + CH 4 reaction agree with the results of earlier crossed-beam experiments at higher collision energy. Although no previous data is available on the product channels of the C( 1 D) + C 2 H 6 reaction, comparison with earlier work involving the same singlet C 3 H 6 potential energy surface allows us to draw conclusions from the measured H-atom yields.