The reactions of atomic carbon in its first excited 1D state with both CH4 and C2H6 have been investigated using a continuous supersonic flow reactor over the 50-296 K temperature range. C(1D) atoms were generated in situ by the pulsed laser photolysis of CBr4 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(1D) + H2 reaction. Although the rate constant for the C(1D) + CH4 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(1D) + C2H6 system decreases as the temperature falls, obeying a capture-type rate law. The H-atom product yields of the C(1D) + CH4 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(1D) + C2H6 reaction, comparison with earlier work involving the same singlet C3H6 potential energy surface allows us to draw conclusions from the measured H-atom yields.
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