Anglada Josep M, Solé Albert
Departament de Química Biològica i Modelització Molecular, IQAC-CSIC , Jordi Girona, 18-26, E-08034 Barcelona, Spain.
Departament de Ciència de Materials i Química Física, i Institut de Química Teòrica i Computacional, Universitat de Barcelona , Martí i Franqués, 1, E-08028 Barcelona, Spain.
J Phys Chem A. 2017 Dec 28;121(51):9698-9707. doi: 10.1021/acs.jpca.7b10715. Epub 2017 Dec 15.
The atmospheric oxidation of nitrous acid by hydroxyl radical, chlorine atom, and chlorine monoxide radical was investigated with high-level theoretical methods. Nitrous acid has two conformers (cis and trans), and we found a reaction path for the oxidation of each of these conformers with the radicals considered. In all cases, the oxidation of the cis conformer is much more favorable than the oxidation of the trans conformer. Interestingly all transition states in these oxidation processes follow a proton-coupled electron-transfer mechanism. Our computed rate constant at 298 K for the reaction of cis-HONO + ·OH is 4.83 × 10 cm molecule s, in excellent agreement with their experimental values (4.85 × 10 and 6.48 × 10 cm molecule s). For the trans-HONO + ·OH reaction our calculated rate constant at 298 K is 9.05 × 10 cm molecule s, and we computed an effective rate constant for the oxidation of the whole nitrous acid by hydroxyl radical of 1.81 × 10 cm molecule s. For the oxidation of nitrous acid by chlorine atom we predict greater rate constants (7.38 × 10, 3.33 × 10, and 2.76 × 10 cm molecule s, for the cis and trans conformers and for the whole HONO), these results suggesting that this reaction should contribute to the tropospheric oxidation of nitrous acid, especially in marine boundary areas, and to the formation of tropospheric ozone. For the oxidation of nitrous acid by chlorine monoxide we predict rate constants roughly 6 orders of magnitude smaller than the oxidation by chlorine atom, and therefore we consider that this process should play a minor role in the troposphere.
采用高精度理论方法研究了亚硝酸被羟基自由基、氯原子和一氧化氯自由基进行的大气氧化反应。亚硝酸有两种构象（顺式和反式），我们找到了每种构象与所考虑的自由基发生氧化反应的一条反应路径。在所有情况下，顺式构象的氧化反应比反式构象的氧化反应更有利。有趣的是，这些氧化过程中的所有过渡态都遵循质子耦合电子转移机制。我们计算得到在298K时顺式-HONO +·OH反应的速率常数为4.83×10 cm³分子⁻¹ s⁻¹，与实验值（4.85×10和6.48×10 cm³分子⁻¹ s⁻¹）非常吻合。对于反式-HONO +·OH反应，我们计算得到在298K时的速率常数为9.05×10 cm³分子⁻¹ s⁻¹，并且我们计算得到羟基自由基氧化整个亚硝酸的有效速率常数为1.81×10 cm³分子⁻¹ s⁻¹。对于氯原子氧化亚硝酸，我们预测的速率常数更大（顺式和反式构象以及整个HONO的速率常数分别为7.38×10、3.33×10和2.76×10 cm³分子⁻¹ s⁻¹），这些结果表明该反应应有助于亚硝酸在对流层中的氧化，特别是在海洋边界区域，并有助于对流层臭氧的形成。对于一氧化氯氧化亚硝酸，我们预测的速率常数比氯原子氧化的速率常数小约6个数量级，因此我们认为该过程在对流层中应起次要作用。
