Kinetic Study of the Gas-Phase O( 1 D) + CH 3 OH and O( 1 D) + CH 3 CN Reactions: Low-Temperature Rate Constants and Atomic Hydrogen Product Yields.

Atomic oxygen in its first excited singlet state, O( 1 D), is an important species in the photochemistry of several planetary atmospheres and has been predicted to be a potentially important reactive species on interstellar ices. Here, we report the results of a kinetic study of the reactions of O( 1 D) with methanol, CH 3 OH, and acetonitrile, CH 3 CN, over the 50-296 K temperature range. A continuous supersonic flow reactor is used to attain these low temperatures coupled with pulsed laser photolysis and pulsed laser-induced fluorescence to generate and monitor O( 1 D) atoms, respectively. Secondary experiments examining the atomic hydrogen product channels of these reactions are also performed, through laser-induced fluorescence measurements of H( 2 S) atom formation. On the kinetic side, the rate constants for these reactions are seen to be large (>2 × 10 -10 cm 3 s -1 ) and consistent with barrierless reactions, although they display contrasting dependences as a function of temperature. On the product formation side, both reactions are seen to yield non-negligible quantities of atomic hydrogen. For the O( 1 D) + CH 3 OH reaction, the derived yields are in good agreement with the conclusions of previous experimental and theoretical works. For the O( 1 D) + CH 3 CN reaction, whose H-atom formation channels had not previously been investigated, electronic structure calculations of several new product formation channels are performed to explain the observed H-atom yields. These calculations demonstrate the barrierless and exothermic nature of the relevant exit channels, confirming that atomic hydrogen is also an important product of the O( 1 D) + CH 3 CN reaction.