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

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 } cm 3 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 CH 3 CO formation pathway in dark molecular clouds, assuming that CH 3 CO is the main reaction product at 10 K. Temperature dependence of the rate coefficient for the OH + CH 3 CHO reaction at ultralow temperatures (11.7-177.5 K): first measurements below 60 K.