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Reactivity of OH and CH3OH between 22 and 64 K: Modelling the Gas Phase Production of CH3O in Barnard 1B

Abstract : In the last years, ultra-low temperature chemical kinetic experiments have demonstrated that some gas-phase reactions are much faster than previously thought. One example is the reaction between OH and CHOH, which has been recently found to be accelerated at low temperatures yielding CHO as main product. This finding opened the question of whether the CHO observed in the dense core Barnard 1b could be formed by the gas-phase reaction of CHOH and OH. Several chemical models including this reaction and grain-surface processes have been developed to explain the observed abundance of CHO with little success. Here we report for the first time rate coefficients for the gas-phase reaction of OH and CHOH down to a temperature of 22 K, very close to those in cold interstellar clouds. Two independent experimental set-ups based on the supersonic gas expansion technique coupled to the pulsed laser photolysis-laser induced fluorescence technique were used to determine rate coefficients in the temperature range 22-64 K. The temperature dependence obtained in this work can be expressed as (22-64 K) = (3.6 ± 0.1) × 10(300 K) cm molecule s. Implementing this expression in a chemical model of a cold dense cloud results in CHO/CHOH abundance ratios similar or slightly lower than the value of ∼ 3 × 10 observed in Barnard 1b. This finding confirms that the gas-phase reaction between OH and CHOH is an important contributor to the formation of interstellar CHO. The role of grain-surface processes in the formation of CHO, although it cannot be fully neglected, remains controversial.
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Submitted on : Wednesday, October 12, 2016 - 1:09:16 PM
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M. Antiñolo, M. Agúndez, Elena Jimenez, B. Ballesteros, André Canosa, et al.. Reactivity of OH and CH3OH between 22 and 64 K: Modelling the Gas Phase Production of CH3O in Barnard 1B. The Astrophysical Journal, American Astronomical Society, 2016, 823 (1), pp.25. ⟨10.3847/0004-637X/823/1/25⟩. ⟨hal-01343402⟩

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