Srinivasan Nanda K, Su Meng-Chih, Sutherland James W, Michael Joe V, Ruscic Branko
Chemistry Division, Argonne National Laboratory, Argonne, Illinois 60439-4831, USA.
J Phys Chem A. 2006 Jun 1;110(21):6602-7. doi: 10.1021/jp057461x.
The motivation for the present study comes from the preceding paper where it is suggested that accepted rate constants for OH + NO2 --> NO + HO2 are high by approximately 2. This conclusion was based on a reevaluation of heats of formation for HO2, OH, NO, and NO2 using the Active Thermochemical Table (ATcT) approach. The present experiments were performed in C2H5I/NO2 mixtures, using the reflected shock tube technique and OH-radical electronic absorption detection (at 308 nm) and using a multipass optical system. Time-dependent profile decays were fitted with a 23-step mechanism, but only OH + NO2, OH + HO2, both HO2 and NO2 dissociations, and the atom molecule reactions, O + NO2 and O + C2H4, contributed to the decay profile. Since all of the reactions except the first two are known with good accuracy, the profiles were fitted by varying only OH + NO2 and OH + HO2. The new ATcT approach was used to evaluate equilibrium constants so that back reactions were accurately taken into account. The combined rate constant from the present work and earlier work by Glaenzer and Troe (GT) is k(OH+NO2) = 2.25 x 10(-11) exp(-3831 K/T) cm3 molecule(-1) s(-1), which is a factor of 2 lower than the extrapolated direct value from Howard but agrees well with NO + HO2 --> OH + NO2 transformed with the updated equilibrium constants. Also, the rate constant for OH + HO2 suitable for combustion modeling applications over the T range (1200-1700 K) is (5 +/- 3) x 10(-11) cm3 molecule(-1) s(-1). Finally, simulating previous experimental results of GT using our updated mechanism, we suggest a constant rate for k(HO2+NO2) = (2.2 +/- 0.7) x 10(-11) cm3 molecule(-1) s(-1) over the T range 1350-1760 K.
本研究的动机源于之前的一篇论文，该论文指出OH + NO2 → NO + HO2公认的速率常数大约高了2倍。这一结论是基于使用活性热化学表（ATcT）方法对HO2、OH、NO和NO2的生成热进行重新评估得出的。本实验在C2H5I/NO2混合物中进行，采用反射激波管技术和OH自由基电子吸收检测（在308 nm处），并使用多程光学系统。随时间变化的轮廓衰减用一个23步的反应机理进行拟合，但只有OH + NO2、OH + HO2、HO2和NO2的解离，以及原子分子反应O + NO2和O + C2H4对衰减轮廓有贡献。由于除前两个反应外的所有反应的准确性都很高，所以通过仅改变OH + NO2和OH + HO2来拟合轮廓。采用新的ATcT方法来评估平衡常数，以便准确考虑逆向反应。本工作与Glaenzer和Troe（GT）早期工作得出的组合速率常数为k(OH+NO2) = 2.25×10(-11) exp(-3831 K/T) cm3 molecule(-1) s(-1)，这比Howard外推的直接值低2倍，但与用更新后的平衡常数转换后的NO + HO2 → OH + NO2很好地吻合。此外，在T范围（1200 - 1700 K）内适用于燃烧模型应用的OH + HO2的速率常数为(5 ± 3)×10(-11) cm3 molecule(-1) s(-1)。最后，使用我们更新后的反应机理模拟GT之前的实验结果，我们建议在1350 - 1760 K的T范围内，k(HO2+NO2)的恒定速率为(2.2 ± 0.7)×10(-11) cm3 molecule(-1) s(-1)。
