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 the molecules in this environment. The knowledge of the rate coefficient of neutral-neutral reactions as a function of temperature,...

The impact of water vapor on the OH reactivity toward CH3CHO at ultra-low temperatures (21.7–135.0 K): Experiments and theory

“…Based on the typical differences (6%) between the mass flow and optical measurements of [CH 3 CHO] 0 , a conservative 10% systematic error can be added to the statistical uncertainties. In the absence of added H 2 O, k obs (T) are in agreement with those previously reported by Blázquez et al 32 for the OH+CH 3 CHO reaction (k(T)) at ultralow temperatures. At the highest temperature, 135 K, however, a slightly higher k obs (T) was found in the present investigation.…”

“…It is recognized for a long time that the clustering process is enhanced and favored at low temperatures. The first step of a clustering process, the dimerization, has been widely discussed in the literature for different organic compounds 31,32,53 At the ultralow temperatures of the present work, formation of (CH 3 CHO) 2 may occur in the timescale of the kinetic experiments when high initial concentrations of CH 3 CHO are introduced in the CRESU chamber.…”

“…Since reaction 1 reduces the amount of "free" acetaldehyde in the cooled jet, the measured rate coefficient can be underestimated. 32,34 For that reason, at first, kinetic studies are performed without added water in a wide concentration range of [CH 3 CHO] 0 in order to identify the threshold of dimerization, which means the acetaldehyde concentration beyond which the pseudo-first order plots start to present a clear downward curvature (see Fig. 3 as an example at 21.7 K).…”

“…The values of f CH 3 CHO were checked offline by measuring the CH 3 CHO concentration in the storage bulb by UV spectroscopy between 240 and 360 nm, as explained by Blázquez et al 32 . In Fig.…”

“…33 The experimental UV system used was described previously. 32,[34][35][36][37] A 30 W deuterium lamp (Oriel, model: Q Series Low Power) was used to irradiate the gas mixture in the absorption cell. The transmitted light was focused on a 0.5 m spectrometer (Chromex 500 is/ms), which has a grating (300 groves per mm with a spectral resolution of 0.19 nm) that disperses the radiation.…”