Liu Yong, Lohr Lawrence L, Barker John R
Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan, Ann Arbor, Michigan 48109-2143, USA.
J Phys Chem A. 2006 Feb 2;110(4):1267-77. doi: 10.1021/jp053099a.
Quasiclassical trajectory calculations are used to investigate the dynamics of the OH(v) + NO(2) --> HONO(2) --> OH(v') + NO(2) recombination/dissociation reaction on an analytic potential energy surface (PES) that gives good agreement with the known structure and vibrational frequencies of nitric acid. The calculated recombination rate constants depend only weakly on temperature and on the initial vibrational energy level of OH(v). The magnitude of the recombination rate constant is sensitive to the potential function describing the newly formed bond and to the switching functions in the PES that attenuate inter-mode interactions at long range. The lifetime of the nascent excited HONO(2) depends strongly not only on its internal energy but also on the identity of the initial state, in disagreement with statistical theory. This disagreement is probably due to the effects of slow intramolecular vibrational energy redistribution (IVR) from the initially excited OH stretching mode. The vibrational energy distribution of product OH(v') radicals is different from statistical distributions, a result consistent with the effects of slow IVR. Nonetheless, the trajectory results predict that vibrational deactivation of OH(v) via the HONO(2) transient complex is approximately 90% efficient, almost independent of initial OH(v) vibrational level, in qualitative agreement with recent experiments. Tests are also carried out using the HONO(2) PES, but assuming the weaker O-O bond strength found in HOONO (peroxynitrous acid). In this case, the predicted vibrational deactivation efficiencies are significantly lower and depend strongly on the initial vibrational state of OH(v), in disagreement with experiments. This disagreement suggests that the actual HOONO PES may contain more inter-mode coupling than found in the present model PES, which is based on HONO(2). For nitric acid, the measured vibrational deactivation rate constant is a useful proxy for the recombination rate, but IVR randomization of energy is not complete, suggesting that the efficacy of the proxy method must be evaluated on a case-by-case basis.
准经典轨迹计算用于研究OH(v) + NO(2) --> HONO(2) --> OH(v') + NO(2)复合/解离反应的动力学，该反应基于一个解析势能面（PES），此势能面与硝酸的已知结构和振动频率吻合良好。计算得到的复合速率常数仅微弱地依赖于温度和OH(v)的初始振动能级。复合速率常数的大小对描述新形成键的势函数以及PES中用于减弱长程模式间相互作用的切换函数很敏感。新生激发态HONO(2)的寿命不仅强烈依赖于其内能，还依赖于初始态的特性，这与统计理论不一致。这种不一致可能是由于最初激发的OH伸缩模式的分子内振动能量再分布（IVR）缓慢所致。产物OH(v')自由基的振动能量分布不同于统计分布，这一结果与缓慢IVR的影响一致。尽管如此，轨迹结果预测通过HONO(2)瞬态复合物使OH(v)振动失活的效率约为90%，几乎与初始OH(v)振动能级无关，这与最近的实验定性相符。还使用了HONO(2)的PES进行测试，但假设在HOONO（过氧亚硝酸）中发现的O - O键强度较弱。在这种情况下，预测的振动失活效率显著更低，并且强烈依赖于OH(v)的初始振动状态，这与实验不一致。这种不一致表明实际的HOONO PES可能比基于HONO(2)的当前模型PES包含更多的模式间耦合。对于硝酸，测量得到的振动失活速率常数是复合速率的一个有用替代指标，但能量的IVR随机化并不完全，这表明替代方法的有效性必须逐例评估。
