Kinetic Study of the Gas-Phase O(1D) + CH3OH and O(1D) + CH3CN Reactions: Low-Temperature Rate Constants and Atomic Hydrogen Product Yields

Atomic oxygen in its first excited singlet state, O­(1D), 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(1D) with methanol, CH3OH, and acetonitrile, CH3CN, 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(1D) atoms, respectively. Secondary experiments examining the atomic hydrogen product channels of these reactions are also performed, through laser-induced fluorescence measurements of H­(2S) atom formation. On the kinetic side, the rate constants for these reactions are seen to be large (>2 × 10–10 cm3 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(1D) + CH3OH reaction, the derived yields are in good agreement with the conclusions of previous experimental and theoretical works. For the O­(1D) + CH3CN 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(1D) + CH3CN reaction.