Theoretical Studies on the Dynamics of Photochemical Processes in Solutions

这项研究始于1991年，目的是为溶液中光化学过程的动力学提供现实的分子模型。对4-（N，N-二甲氨基）苯甲腈（DMABN）的Norrish II型反应和光诱导电荷转移态形成反应进行了分子动力学（MD）计算。对于Norrish II型反应，研究了丁醛衍生的1，4-双自由基中间体的电子弛豫机理。采用从头算方法计算了单重态和三重态双自由基的势能面以及它们之间的自旋轨道耦合元。对甲醇溶液中的双自由基进行了分子动力学计算，得到了三重态-单重态跃迁的速率常数。结果与实验结果一致。对于DMABN的光诱导电子转移反应，通过假设溶剂运动的谐振浴模型，推导出了一个新的反应表面哈密顿量和溶剂化坐标。MD计算被用来获得各种数量包括在哈密顿量，如自由能表面，有效质量的溶剂化坐标和摩擦内核的溶剂松弛。进行了随机轨道计算，以获得反应速率。

This research started in 1991 with the aim to provide realistic molecular models for the dynamics of photochemical processes in solutions. We have carried out the molecular dynamics (MD) calculations for the Norrish type II reaction and the photo-induced charge transfer state formation reaction of 4-(N,N-dimethylamino)benzonitrile(DMABN). For the Norrish type II reaction, the mechanism of electronic relaxation of 1,4-diradical intermediate derived from butanal was examined. The ab initio calculations were performed to obtaine the potential energy surfaces of singlet and triplet diradicals and the spin-orbit coupling element between them. The MD calculations for the diradical in methanol solution were carried out to obtain the rate constant for the triplet-singlet transition. The results were consistent with the experimental findings. For the photo-induced electron transfer reaction of DMABN, we derived a new reaction surface Hamiltonian for the torsional mode of dimethylamino group and the solvation coordinate by assuming the harmonic bath model for the solvent motions. The MD calculations were utilized to obtain various quantities included in the Hamiltonian such as the free energy surface, the effective mass for the solvation coordinate and the friction kernel for the solvent relaxation. The stochastic trajectory calculations were carried out to obtain the reaction rate.