Huang Shang-Chen, Nghia N T, Putikam Raghunath, Nguyen Hue M T, Lin M C, Tsuchiya Soji, Lee Yuan-Pern
Department of Applied Chemistry and Institute of Molecular Science, National Chiao Tung University, Hsinchu 30010, Taiwan.
School of Chemical Engineering - Hanoi University of Science and Technology, Hanoi, Vietnam.
J Chem Phys. 2014 Oct 21;141(15):154313. doi: 10.1063/1.4897418.
We investigated the reaction dynamics of O((1)D) towards hydrogen atoms of two types in HCOOH. The reaction was initiated on irradiation of a flowing mixture of O3 and HCOOD or DCOOH at 248 nm. The relative vibration-rotational populations of OH and OD (1 ≦ v ≦ 4, J ≤ 15) states were determined from time-resolved IR emission recorded with a step-scan Fourier-transform spectrometer. In the reaction of O((1)D) + HCOOD, the rotational distribution of product OH is nearly Boltzmann, whereas that of OD is bimodal. The product ratio [OH]/[OD] is 0.16 ± 0.05. In the reaction of O((1)D) + DCOOH, the rotational distribution of product OH is bimodal, but the observed OD lines are too weak to provide reliable intensities. The three observed OH/OD channels agree with three major channels of production predicted with quantum-chemical calculations. In the case of O((1)D) + HCOOD, two intermediates HOC(O)OD and HC(O)OOD are produced in the initial C-H and O-D insertion, respectively. The former undergoes further decomposition of the newly formed OH or the original OD, whereas the latter produces OD via direct decomposition. Decomposition of HOC(O)OD produced OH and OD with similar vibrational excitation, indicating efficient intramolecular vibrational relaxation, IVR. Decomposition of HC(O)OOD produced OD with greater rotational excitation. The predicted [OH]/[OD] ratio is 0.20 for O((1)D) + HCOOD and 4.08 for O((1)D) + DCOOH; the former agrees satisfactorily with experiments. We also observed the v3 emission from the product CO2. This emission band is deconvoluted into two components corresponding to internal energies E = 317 and 96 kJ mol(-1) of CO2, predicted to be produced via direct dehydration of HOC(O)OH and secondary decomposition of HC(O)O that was produced via decomposition of HC(O)OOH, respectively.
我们研究了O((1)D)与HCOOH中两种类型氢原子的反应动力学。该反应通过在248 nm波长下辐照O3与HCOOD或DCOOH的流动混合物引发。利用步进扫描傅里叶变换光谱仪记录的时间分辨红外发射，确定了OH和OD（1≦v≦4，J≤15）态的相对振动转动布居。在O((1)D) + HCOOD反应中，产物OH的转动分布接近玻尔兹曼分布，而OD的转动分布是双峰的。产物比[OH]/[OD]为0.16±0.05。在O((1)D) + DCOOH反应中，产物OH的转动分布是双峰的，但观测到的OD谱线太弱，无法提供可靠的强度。观测到的三个OH/OD通道与量子化学计算预测的三个主要生成通道相符。在O((1)D) + HCOOD反应中，最初的C-H和O-D插入分别生成了两种中间体HOC(O)OD和HC(O)OOD。前者通过新形成的OH或原始的OD进一步分解，而后者通过直接分解产生OD。HOC(O)OD的分解产生了具有相似振动激发的OH和OD，表明存在有效的分子内振动弛豫（IVR）。HC(O)OOD的分解产生了具有更大转动激发的OD。对于O((1)D) + HCOOD，预测的[OH]/[OD]比为0.20，对于O((1)D) + DCOOH为4.08；前者与实验结果令人满意地相符。我们还观测到了产物CO2的v3发射。该发射带被解卷积为两个组分，分别对应于CO2的内能E = 317和96 kJ·mol(-1)，预计分别通过HOC(O)OH的直接脱水和HC(O)OOH分解产生的HC(O)O的二次分解产生。
