Theoretische Chemie, Fakultät für Chemie, Universität Bielefeld, Universitätsstr. 25, D-33615 Bielefeld, Germany.
J Phys Chem A. 2011 Jun 16;115(23):5992-6001. doi: 10.1021/jp1103998. Epub 2011 Feb 10.
The photodissociation of methyl iodide in the A band is studied by full-dimensional (9D) wave packet dynamics calculations using the multiconfigurational time-dependent Hartree approach. The potential energy surfaces employed are based on the diabatic potentials of Xie et al. [J. Phys. Chem. A 2000, 104, 1009] and the vertical excitation energy is taken from recent ab initio calculations [Alekseyev et al. J. Chem. Phys.2007, 126, 234102]. The absorption spectrum calculated for exclusively parallel excitation agrees well with the experimental spectrum of the A band. The electronic population dynamics is found to be strongly dependent on the motion in the torsional coordinate related to the H(3)-C-I bend, which presumably is an artifact of the diabatic model employed. The calculated fully product state-selected partial spectra can be interpreted based on the reflection principle and suggests strong coupling between the C-I stretching and the H(3)-C-I bending motions during the dissociation process. The computed rotational and vibrational product distributions typically reproduce the trends seen in the experiment. In agreement with experiment, a small but significant excitation of the total symmetric stretching and the asymmetric bending modes of the methyl fragment can be seen. In contrast, the umbrella mode of the methyl is found to be too highly excited in the calculated distributions.
采用多组态含时哈特ree 方法的全维（9D）波包动力学计算研究了 A 带中碘化甲基的光解。所采用的势能面基于谢等人的离域势能[J. Phys. Chem. A 2000, 104, 1009]，垂直激发能取自最近的从头算计算[Alekseyev 等人，J. Chem. Phys.2007, 126, 234102]。仅平行激发的吸收光谱与 A 带的实验光谱吻合得很好。电子布居动力学发现强烈依赖于与 H（3）-C-I 弯曲相关的扭转坐标的运动，这可能是所采用的离域模型的人为产物。计算的完全产物态选择的部分光谱可以基于反射原理进行解释，并表明在解离过程中 C-I 伸缩和 H（3）-C-I 弯曲运动之间存在强耦合。计算得到的转动和振动产物分布通常再现了实验中观察到的趋势。与实验一致，可看到甲基片段的总对称伸缩和不对称弯曲模式的小但显著的激发。相比之下，在计算分布中发现甲基的伞形模式被过度激发。
