OH(²Π) + C₂H₄ Reaction: A Combined Crossed Molecular Beam and Theoretical Study

Abstract

The reaction between the ground-state hydroxyl radical, OH(2Π), and ethylene, C2H4, has been investigated under single-collision conditions by the crossed molecular beam scattering technique with mass-spectrometric detection and time-of-flight analysis at the collision energy of 50.4 kJ/mol. Electronic structure calculations of the underlying potential energy surface (PES) and statistical Rice–Ramsperger–Kassel–Marcus (RRKM) calculations of product branching fractions on the derived PES for the addition pathway have been performed. The theoretical results indicate a temperature-dependent competition between the anti-/syn-CH2CHOH (vinyl alcohol) + H, CH3CHO (acetaldehyde) + H, and H2CO (formaldehyde) + CH3 product channels. The yield of the H-abstraction channel could not be quantified with the employed methods. The RRKM results predict that under our experimental conditions, the anti- and syn-CH2CHOH + H product channels account for 38% (in similar amounts) of the addition mechanism yield, the H2CO + CH3 channel for ∼58%, while the CH3CHO + H channel is formed in negligible amount (<4%). The implications for combustion and astrochemical environments are discussed.

Theoretical investigation of the OH-initiated atmospheric degradation mechanism of CX2CHX (X = H, F, Cl) by advanced quantum chemical and transition state theory methods

“…As already mentioned, several quantum chemical studies are available in the literature for the prototypical reaction between OH and ethylene, 64,70,72,73 with the most detailed and accurate analyses being probably those performed in 2006 by Senosiain et al 70 and Cleary et al 64 An inspection of the different results summarized in Table 1 shows that all the computational approaches provide comparable trends, and, in particular, the jChS relative energies computed in this work are in good agreement (<1 kcal mol −1 ) with the other high-level ones of ref. 64 and 70.…”

“…The reaction between CH 2 CH 2 and OH has already been deeply studied over the years both experimentally 64–69 and theoretically, 48,70–73 serving more than once as a benchmark for exploring a variety of either similar reactions of unsaturated olefins or diverse theoretical techniques. As already pointed out, it will serve the same purpose in the current study also.…”

Rotational Spectrum and First Interstellar Detection of 2-methoxyethanol Using ALMA Observations of NGC 6334I

“…Once formed through this route, the 2-hydroxyethyl radical is submerged in a notable >100 kJ mol −1 potential well. As demonstrated by Liang et al (2023), this radical may therefore be quite efficiently produced via the gaseous radiative association of OH and C 2 H 4 in colder interstellar conditions. Alternatively, 2-methoxyethanol could also be formed via the radical-radical recombination reaction of CH 2 OH and the methoxymethyl radical…”

“…Another formation route of this radical is the reaction of OH and ethylene (C 2 H 4 ). In fact, the addition of the OH radical into the π orbital of the C=C bond of ethylene has been shown to have no overall energetic barrier (Liang et al 2023),…”