Departamento de Química Física, Facultad de Ciencias y Tecnologías Químicas, Universidad de Castilla-La Mancha, Avda. Camilo José Cela, 1B, 13071 Ciudad Real, Spain.
Phys Chem Chem Phys. 2019 Mar 27;21(13):6942-6957. doi: 10.1039/c9cp00439d.
The reactivity of methanol (CH3OH) toward the hydroxyl (OH) radical was investigated in the temperature range 11.7-177.5 K using the CRESU (French acronym for Reaction Kinetics in a Uniform Supersonic Flow) technique. In the present study, the temperature dependence of the rate coefficient for the OH + CH3OH reaction, k(T), has been revisited and additional experimental and computational data are reported. New kinetic measurements were performed to fill the existing gaps (<22 K, 22-42 K and 88-123 K), reporting k(T < 20 K) for the first time. The lowest temperature ever achieved by a pulsed CRESU has been obtained in this work (11.7 K). k(T) abruptly increases by almost 2 orders of magnitude from 177.5 K to around 100 K. At T < 100 K, this increase is less pronounced, reaching the capture limit at temperatures below 22 K. The pressure dependence of k(T) has been investigated for selected temperatures and gas densities (1.5 × 1016 to 4.3 × 1017 cm-3), combining our results with those previously reported. No dependence was observed within the experimental uncertainties below 110 K. The high- and low-pressure rate coefficients, kHPL(T) and kLPL(T), were also studied in detail using high-level quantum chemical and theoretical kinetic methodologies, closely reproducing the experimental data between 20 and 400 K. The results suggest that the experimental data are near the high pressure limit at the lowest temperatures, but that the reaction remains a fast and effective source of CH2OH and CH3O at the low pressures and temperatures prevalent in the interstellar medium.
使用 CRESU（法国统一超声速流反应动力学的首字母缩写）技术，在 11.7-177.5 K 的温度范围内研究了甲醇（CH3OH）与羟基（OH）自由基的反应性。在本研究中，重新考察了 OH + CH3OH 反应的速率系数 k(T)随温度的变化关系，并报告了额外的实验和计算数据。进行了新的动力学测量以填补现有空白（<22 K、22-42 K 和 88-123 K），首次报告了 k(T < 20 K)的数据。本工作获得了 CRESU 技术有史以来达到的最低温度（11.7 K）。k(T)在 177.5 K 到 100 K 左右急剧增加近 2 个数量级。在 T < 100 K 时，这种增加不太明显，在温度低于 22 K 时达到捕获极限。在选定的温度和气体密度（1.5 × 1016 到 4.3 × 1017 cm-3）下，研究了 k(T)的压力依赖性，将我们的结果与之前报道的结果结合起来。在 110 K 以下的实验不确定度范围内没有观察到依赖性。还使用高级量子化学和理论动力学方法详细研究了高低压速率系数 kHPL(T)和 kLPL(T)，在 20-400 K 之间紧密再现了实验数据。结果表明，在最低温度下，实验数据接近高压极限，但在星际介质中普遍存在的低压和低温下，该反应仍然是 CH2OH 和 CH3O 的快速有效来源。
