Kinetic study of the OH + ethylene reaction using frequency‐modulated laser absorption spectroscopy

Abstract

The pressure dependence of the OH + C2H4 addition reaction has been investigated using frequency‐modulated laser absorption spectroscopy to monitor OH kinetics. Bimolecular rate coefficients for the title reaction are reported in argon bath gas at room temperature and total pressures ranging from 2 to 361 Torr. The pressure‐dependent rate coefficients measured here agree well with the majority of published kinetic studies under similar conditions. Previous high‐level ab initio calculations have identified a prereaction complex on the OH + C2H4 potential energy surface. The influence of this complex on the OH + C2H4 kinetics has been investigated using one‐dimensional master equation analyses of the current and previous experimental measurements.

Dissociative Photodetachment Dynamics of the OH–(C2H4) Anion Complex

“…The hydroxyl radical is also one of the dominant species involved in the atmospheric oxidation of alkenes leading to formation of a radical adduct which can then be further oxidized . The decomposition of this adduct is important in hydrocarbon flames because it is the dominant source of ethanol. − As a result, numerous kinetic-based − and dynamics studies − have been performed on this system.…”

Direct Trace Fitting of Experimental Data Using the Master Equation: Testing Theory and Experiments on the OH + C2H4 Reaction

“…When it is released into the atmosphere, the gas-phase oxidation of ethylene, predominantly initiated by the reaction with hydroxyl radicals, is the major removal process. Ethylene has a relatively short lifetime, τ, with respect to the removal by OH radicals (τ ∼ 6–30 h) and represents a significant atmospheric OH sink. − At low temperatures ( T ≤ 500 K), the ethylene + OH reaction proceeds via a pressure-dependent OH addition to the π-bond (R1), which is an important reaction in both atmospheric , and combustion chemistry. , …”

“…Ethylene has a relatively short lifetime, τ, with respect to the removal by OH radicals (τ ∼ 6−30 h) and represents a significant atmospheric OH sink. 7−9 At low temperatures (T ≤ 500 K), the ethylene + OH reaction proceeds via a pressure-dependent OH addition to the π-bond (R1), which is an important reaction in both atmospheric 7,10 and combustion chemistry. 11,12 However, at elevated temperatures (T > 600 K), the abstraction of a hydrogen atom becomes significant and eventually turns into the major channel of this reaction.…”

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

“…Kinetic experiments have been performed to obtain information on the rate coefficients and their dependence on temperature and pressure, − and kinetic and photochemical investigations to derive product branching fractions have also been reported. − Additionally, theoretical calculations have been carried out to derive the relevant potential energy surface (PES) and to obtain a theoretical estimate of the rate coefficients through high-level ab initio electronic structure and kinetic (statistical) calculations. − According to these studies, the OH + C 2 H 4 reaction can proceed through two different mechanisms, that is, either by the H-abstraction mechanism, leading to the formation of a water molecule and the vinyl radical (C 2 H 3 ), or by the addition mechanism of the OH radical to the CC double bond of ethylene. While the direct abstraction process exhibits a sizeable entrance energy barrier, the addition process appears to be barrierless and is characterized by the initial formation of a pre-reactive van der Waals complex, which leads to the formation of the C 2 H 4 OH (2-hydroxyethyl) covalently bound radical intermediate through a submerged barrier.…”