Gas-phase kinetics of CH3CHO with OH radicals between 11.7 and 177.5 K

Abstract

Gas-phase reactions in the interstellar medium (ISM) are a source of molecules in this environment. The knowledge of the rate coefficient for neutral–neutral reactions as a function of temperature, k(T), is essential to improve astrochemical models. In this work, we have experimentally measured k(T) for the reaction between the OH radical and acetaldehyde, both present in many sources of the ISM. Laser techniques coupled to a CRESU system were used to perform the kinetic measurements. The obtained modified Arrhenius equation is k(T = 11.7–177.5 K) = (1.2 ± 0.2) × 10⁻¹¹ (T/300 K)^{−(1.8±0.1)} exp–{(28.7 ± 2.5)/T} cm³ molecule⁻¹ s⁻¹. The k(T) value of the title reaction has been measured for the first time below 60 K. No pressure dependence of k(T) was observed at ca. 21, 50, 64 and 106 K. Finally, a pure gas-phase model indicates that the title reaction could become the main CH₃CO formation pathway in dark molecular clouds, assuming that CH₃CO is the main reaction product at 10 K.