Church Jonathan R, Vaida Veronica, Skodje Rex T
Department of Chemistry, University of Colorado, Boulder, Colorado 80309-0215, United States.
J Phys Chem A. 2021 Mar 25;125(11):2232-2242. doi: 10.1021/acs.jpca.0c10475. Epub 2021 Mar 11.
Gas-phase reactions between pyruvic acid (PA) and HO radicals were examined using ab initio quantum chemistry and transition state theory. The rate coefficients were determined over a temperature range of 200-400 K including tunneling contributions. Six potential reaction pathways were identified. The two hydrogen abstraction reactions yielding the HO product were found to have high barriers. The HO radical was also found to have a catalytic effect on the intramolecular hydrogen transfer reactions occurring by three distinct routes. These hydrogen-shift reactions are very interesting mechanistically although they are highly endothermic. The only reaction that contributes significantly to the consumption of PA is a multistep pathway involving a peroxy-radical intermediate, PA + HO → CHCOOH + OH + CO. This exothermic process has potential atmospheric relevance because it produces an OH radical as a product. Atmospheric models currently have difficulty predicting accurate OH concentrations for certain atmospheric conditions, such as environments free of NOx and the nocturnal boundary layer. Reactions of this sort, although not necessary with PA, may account for a portion of this deficit. The present study helps settle the issue of the relative roles of reaction and photolysis in consumption of PA in the troposphere.
利用从头算量子化学和过渡态理论研究了丙酮酸（PA）与羟基自由基（HO）之间的气相反应。在200 - 400 K的温度范围内确定了速率系数，其中包括隧穿贡献。确定了六条潜在的反应途径。发现生成HO产物的两个氢提取反应具有较高的势垒。还发现HO自由基对通过三种不同途径发生的分子内氢转移反应具有催化作用。这些氢转移反应虽然高度吸热，但在机理上非常有趣。唯一对PA消耗有显著贡献的反应是一条涉及过氧自由基中间体的多步途径，即PA + HO → CHCOOH + OH + CO。这个放热过程具有潜在的大气相关性，因为它产生了一个OH自由基作为产物。大气模型目前在预测某些大气条件下的准确OH浓度方面存在困难，例如没有氮氧化物的环境和夜间边界层。这类反应，虽然不一定是与PA发生的反应，可能是造成这一不足的部分原因。本研究有助于解决对流层中PA消耗过程中反应和光解相对作用的问题。
