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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Unimolecular Reaction Rate Constants of NO_2 Just above D_0
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Unimolecular Reaction Rate Constants of NO_2 Just above D_0

机译：D_0上方NO_2的单分子反应速率常数

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Photoinitiated unimolecular decomposition on a barrierless potential energy surface (PES) has been studied for the reaction NO_2 -> O(~3P_2) + NO(X~2#PI#_(1/2), v = 0) for excess energies up to approximately 17 cm~(-1) above the dissociation threshold (i.e., D_0 for nonrotating molecules) by using expansion-cooled samples and the time-resolved pump-probe technique. To examine the threshold region with enough energy resolution to discern abrupt changes in the rate constant, should they occur, a pump-probe cross-correlation temporal width of approx 25 ps and a pump line width <= 2 cm~(-1) has been used. These are the first direct observations of the reaction rate constants in this energy regime. The rate constant was found to increase by an order of magnitude, varying from approx 2 * 10~(10) s~(-1) to >= 10~(11) s~(-1), the latter being a rough lower bound imposed by the experimental arrangement. The rate constant does not display the energy dependence predicted by using phase space theory, at least in detail. Rather, it appears to reflect the highly complex nature of the levels and the multiple PESs that are believed to be responsible for the anomalously high vibronic level density which has been observed just below D_0. These results bridge the gap between spectroscopic studies which have been carried out at energies just above D_0 and ultrafast experiments which have measured rate constants in this energy region with pump laser spectral widths of approx 30 cm~(-1).
机译：对于NO_2-> O（〜3P_2）+ NO（X〜2＃PI #_（1/2），v = 0）的过量能量上升，已经研究了无障碍势能表面（PES）上光引发的单分子分解通过使用膨胀冷却的样品和时间分辨的泵浦探针技术，可将其解离阈值（即非旋转分子的D_0）高出解离阈值约17 cm〜（-1）。为了检查阈值区域是否具有足够的能量分辨率以辨别速率常数的突然变化，如果出现这些变化，则大约25 ps的泵浦探针互相关时间宽度和<= 2 cm〜（-1）的泵浦线宽度被使用。这些是在该能量范围内对反应速率常数的首次直接观察。发现速率常数增加了一个数量级，从大约2 * 10〜（10）s〜（-1）到> = 10〜（11）s〜（-1），后者大致较低实验安排施加的约束。速率常数至少没有详细显示出使用相空间理论预测的能量依赖性。相反，它似乎反映了水平的高度复杂性以及多个PES，它们被认为是导致刚好在D_0以下观察到的异常高振动水平的原因。这些结果弥合了在D_0以上的能量下进行的光谱研究与超快实验之间的差距，超快实验已在该能量范围内以大约30 cm〜（-1）的泵浦激光光谱宽度测量了速率常数。

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