光解动力学半经典Wigner处理的新认识
New insights into the semiclassical Wigner treatment of photodissociation dynamics
摘要：
Brown和Heller的\emph{semiclassical Wigner treatment} [J.Chem.Phys.75，186（1981）]被应用于三原子直接光离解，目的是以相对低的计算成本精确地预测最终态分布，并具有可用的强有力的解释工具。第一次，治疗是全方位的。所提出的公式尽可能地与量子描述密切平行。提出了一个近似的版本，这仍然是准确的，而数值上更有效。除了被通常的振动维格纳分布加权，最终的相空间状态似乎是由新的\emph{rotational Wigner distributions}加权。这些密度具有显著的结构，清楚地表明，对旋转态$j$贡献最大的经典轨迹是那些到达旋转角动量接近$[j(j+1)]^{1/2}$（以$\hbar$为单位）的产物的轨迹。以前的方法涉及从试剂分子到产物的运行轨迹。替代的\emph{backward approach} [L. Bonnet，J.Chem.Phys.133，174108（2010）]，其中轨迹在相反方向上运行，被示出除了\emph{state-selective}之外，还极大地提高了最严格方法的数值效率，并且因此理想地适合于描述在速度成像实验中测量的状态相关分布。用上述方法得到的结果与Guo的碘甲烷光解的类三原子模型[J. Chem. Phys. 96，6629（1992）]的严格量子结果进行了比较，发现惊人的一致性，相比之下，Goursaud的标准方法\emph{et al.} [J. Chem. Phys. 65，5453（1976）]只是半定量的。
英文摘要：
The \emph{semiclassical Wigner treatment} of Brown and Heller [J. Chem. Phys. 75, 186 (1981)] is applied to triatomic direct photodissociations with the aim of accurately predicting final state distributions at relatively low computational cost, and having available a powerful interpretative tool. For the first time, the treatment is full-dimensional. The proposed formulation closely parallels the quantum description as far as possible. An approximate version is proposed, which is still accurate while numerically much more efficient. In addition to be weighted by usual vibrational Wigner distributions, final phase space states appear to be weighted by new \emph{rotational Wigner distributions}. These densities have remarkable structures clearly showing that classical trajectories most contributing to rotational state $j$ are those reaching the products with a rotational angular momentum close to $[j(j+1)]^{1/2}$ (in $\hbar$ unit). The previous methods involve running trajectories from the reagent molecule onto the products. The alternative \emph{backward approach} [L. Bonnet, J. Chem. Phys. 133, 174108 (2010)], in which trajectories are run in the reverse direction, is shown to strongly improve the numerical efficiency of the most rigorous method in addition to be \emph{state-selective}, and thus, ideally suited to the description of state-correlated distributions measured in velocity imaging experiments. The results obtained by means of the previous methods are compared with rigorous quantum results in the case of Guo's triatomic-like model of methyl iodide photodissociation [J. Chem. Phys. 96, 6629 (1992)] and an astonishing agreement is found. In comparison, the standard method of Goursaud \emph{et al.} [J. Chem. Phys. 65, 5453 (1976)] is only semi-quantitative.
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