Klippenstein S J, Harding L B, Ruscic B, Sivaramakrishnan R, Srinivasan N K, Su M-C, Michael J V
Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, Illinois 60439, USA.
J Phys Chem A. 2009 Sep 24;113(38):10241-59. doi: 10.1021/jp905454k.
Primary and secondary reactions involved in the thermal decomposition of NH2OH are studied with a combination of shock tube experiments and transition state theory based theoretical kinetics. This coupled theory and experiment study demonstrates the utility of NH2OH as a high temperature source of OH radicals. The reflected shock technique is employed in the determination of OH radical time profiles via multipass electronic absorption spectrometry. O-atoms are searched for with atomic resonance absorption spectrometry. The experiments provide a direct measurement of the rate coefficient, k1, for the thermal decomposition of NH2OH. Secondary rate measurements are obtained for the NH2 + OH (5a) and NH2OH + OH (6a) abstraction reactions. The experimental data are obtained for temperatures in the range from 1355 to 1889 K and are well represented by the respective rate expressions: log[k/(cm3 molecule(-1) s(-1))] = (-10.12 +/- 0.20) + (-6793 +/- 317 K/T) (k1); log[k/(cm3 molecule(-1) s(-1))] = (-10.00 +/- 0.06) + (-879 +/- 101 K/T) (k5a); log[k/(cm3 molecule(-1) s(-1))] = (-9.75 +/- 0.08) + (-1248 +/- 123 K/T) (k6a). Theoretical predictions are made for these rate coefficients as well for the reactions of NH2OH + NH2, NH2OH + NH, NH + OH, NH2 + NH2, NH2 + NH, and NH + NH, each of which could be of secondary importance in NH2OH thermal decomposition. The theoretical analyses employ a combination of ab initio transition state theory and master equation simulations. Comparisons between theory and experiment are made where possible. Modest adjustments of predicted barrier heights (i.e., by 2 kcal/mol or less) generally yield good agreement between theory and experiment. The rate coefficients obtained here should be of utility in modeling NOx in various combustion environments.
采用激波管实验和基于过渡态理论的理论动力学相结合的方法，研究了羟胺热分解过程中的一级和二级反应。这种理论与实验相结合的研究证明了羟胺作为高温羟基自由基源的实用性。采用反射激波技术，通过多程电子吸收光谱法测定羟基自由基的时间分布。用原子共振吸收光谱法寻找氧原子。实验直接测量了羟胺热分解的速率系数k1。还获得了NH2 + OH (5a) 和NH2OH + OH (6a) 夺氢反应的二级速率测量结果。实验数据是在1355至1889 K的温度范围内获得的，并且分别由各自的速率表达式很好地表示：log[k/(cm3 molecule(-1) s(-1))] = (-10.12 +/- 0.20) + (-6793 +/- 317 K/T) (k1)；log[k/(cm3 molecule(-1) s(-1))] = (-10.00 +/- 0.06) + (-879 +/- 101 K/T) (k5a)；log[k/(cm3 molecule(-1) s(-1))] = (-9.75 +/- 0.08) + (-1248 +/- 123 K/T) (k6a)。对这些速率系数以及NH2OH + NH2、NH2OH + NH、NH + OH、NH2 + NH2、NH2 + NH和NH + NH反应进行了理论预测，每个反应在羟胺热分解中可能具有次要重要性。理论分析采用了从头算过渡态理论和主方程模拟相结合的方法。在可能的情况下对理论和实验进行了比较。对预测的势垒高度进行适度调整（即2 kcal/mol或更小）通常会使理论和实验之间取得良好一致。这里获得的速率系数在模拟各种燃烧环境中的氮氧化物时应该是有用的。
