Assessing the Role of Water Monomer in the Atmospheric OH-Initiated Oxidation of Ethylene Oxide

IF 2.6 3区化学 Q2 CHEMISTRY, MULTIDISCIPLINARY

ACS Earth and Space Chemistry Pub Date : 2026-09-17 Epub Date: 2026-08-21 DOI:10.1021/acsearthspacechem.6c00196

Daniel Moura, Joel Leitão Nascimento, Tiago Vinicius Alves

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Abstract

The atmospheric oxidation of ethylene oxide (EtO) by hydroxyl radicals (OH) plays a key role in determining its environmental fate, yet the influence of water vapor on this process remains poorly understood. Here, we present a detailed theoretical investigation of both gas-phase and water-mediated mechanisms for the EtO + OH reaction. A comprehensive exploration of the potential energy surface was performed at the M06-2X/def2-TZVPP level, revealing the formation of prereactive complexes and multiple reaction pathways, including cooperative effects induced by a single water molecule. Kinetic parameters were evaluated using canonical variational theory with small-curvature tunneling (CVT/SCT) within a pre-equilibrium framework. The calculated gas-phase rate constants are in excellent agreement with recent experimental measurements. Effective rate constants, obtained by incorporating atmospheric water concentrations, indicate that the contribution of water-assisted pathways remains minor over the 200–400 K temperature range. Under typical tropospheric conditions, the oxidation process is therefore dominated by the gas-phase mechanism.

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评价水单体在环氧乙烷大气氢氧氧化中的作用

环氧乙烷（EtO）在大气中被羟基自由基（OH）氧化在决定其环境命运中起着关键作用，然而水蒸气对这一过程的影响仍然知之甚少。在这里，我们对EtO + OH反应的气相和水介导机制进行了详细的理论研究。在M06-2X/def2-TZVPPlevel上对势能面进行了全面的探索，揭示了反应前配合物的形成和多种反应途径，包括单个水分子诱导的协同效应。在预平衡框架下，利用正则变分理论对小曲率隧道（CVT/SCT）的动力学参数进行了评估。计算的气相速率常数与最近的实验测量结果非常吻合。通过纳入大气水浓度得到的有效速率常数表明，在200-400 K温度范围内，水辅助途径的贡献仍然很小。因此，在典型的对流层条件下，氧化过程由气相机制主导。

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来源期刊

ACS Earth and Space Chemistry Earth and Planetary Sciences-Geochemistry and Petrology

CiteScore

5.30

自引率

11.80%

发文量

249

期刊介绍： The scope of ACS Earth and Space Chemistry includes the application of analytical, experimental and theoretical chemistry to investigate research questions relevant to the Earth and Space. The journal encompasses the highly interdisciplinary nature of research in this area, while emphasizing chemistry and chemical research tools as the unifying theme. The journal publishes broadly in the domains of high- and low-temperature geochemistry, atmospheric chemistry, marine chemistry, planetary chemistry, astrochemistry, and analytical geochemistry. ACS Earth and Space Chemistry publishes Articles, Letters, Reviews, and Features to provide flexible formats to readily communicate all aspects of research in these fields.