ABSTRACT Up to now, more than 200 molecular species have been detected by the astronomers using ground-based and space-based telescopes within the cold (T<100 K) regions of the so-called interstellar medium (ISM). The hydroxyl (OH) radical is ubiquitous in most of these observations, as well as other molecules such as formaldehyde (H2CO), methanol (CH3OH), and ethanol (CH3CH2OH). The chemistry in such regions of the ISM requires the knowledge of reliable rate coefficients from laboratory data to interpret the astronomical observations in terms of abundances relative to H nuclei, the most abundant species in the ISM. In this review, the current results on the gas-phase kinetics of reactions of the OH radical with H2CO, CH3OH and CH3CH2OH at T<202 K are presented. In these studies, to generate a uniform well-controlled cold environment and performing the kinetic experiments, the CRESU (French acronym of Cinétique de Réaction en Ecoulement Supersonique Uniforme) technique is mostly employed. This technique is based on a continuous or pulsed supersonic expansion of a gas from a high-pressure reservoir to a low-pressure chamber through a “tunable” Laval nozzle coupled to different detection methods such as laser-based techniques. The pulsed CRESU technique has been used by the UCLM research group to study chemical kinetics at ultralow temperatures (T = 11.7 ‑ 177.5 K). This apparatus achieves the lowest temperature ever reached with a pulsed CRESU, 11.7 K. The reviewed results have important implications in the interdisciplinary field of Astrochemistry as an enhancement of the rate coefficient for the title reactions has been observed, providing more realistic data than those derived from extrapolation of temperature dependencies obtained at high temperatures usually employed in astrochemical models in the absence of low temperature data. In addition, these kinetic results help to shed some light on the astronomical observations of HCO and CH3O radicals in dark molecular clouds of the ISM.
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