甲基乙烯基克里奇中间体的激发态动力学：不同的圆锥交叉点决定顺反构型的不同无辐射弛豫通道

本文为了揭示甲基乙烯基克里奇中间体(MVCI)的不同异构体的光化学过程的异同，进而深入理解甲基和乙烯基的不同贡献，在多参考态完全活化空间CASSCF和多参考态二阶微扰理论CASPT2水平开展了电子结构计算，并基于CASSCF方法进行了轨线面跃迁非绝热动力学模拟.结果表明，从第一激发态S₁出发的优势反应通道为关环为双环氧乙烷的过程，其中，围绕C-O键为顺式的两种构型关环进度明显慢于反式，说明了乙烯基上的氢与端位氧原子间形成的分子内氢键约束了C-O键的旋转. 更为重要的是，首次在克里奇中间体的光化学中发现，甲基和乙烯基两个重基团的协同作用造成C3原子处呈明显的三角锥化，进而在垂直区域导致两个结构不同、分别趋近顺式和反式构型的势能面交叉点. 从不同初始构型出发的轨线，其无辐射跃迁对两类不同交叉点的偏好造成了各构型间显著不同的动力学行为.

Photodynamics of Methyl-Vinyl Criegee Intermediate: Different Conical Intersections Govern the Fates of Syn/Anti Con gurations

Methyl vinyl ketone oxide, an unsaturated four-carbon Criegee intermediate produced from the ozonolysis of isoprene has been recognized to play a key role in determining the tropospheric OH concentration. It exists in four configurations (anti-anti, anti-syn, syn-anti, and syn-syn) due to two different substituents of saturated methyl and unsaturated vinyl groups. In this study, we have carried out the electronic structure calculation at the multi-configurational CASSCF and multi-state MS-CASPT2 levels, as well as the trajectory surface-hopping nonadiabatic dynamics simulation at the CASSCF level to reveal the different fates of syn/anti configurations in photochemical process. Our results show that the dominant channel for the S₁-state decay is a ring closure, isomerization to dioxirane, during which, the syn(C-O) con guration with an intramolecular hydrogen bond shows slower nonadiabatic photoisomerization. More importantly, it has been found for the first time in photochemistry of Criegee intermediate that the cooperation of two heavy groups (methyl and vinyl) leads to an evident pyramidalization of C3 atom in methyl-vinyl Criegee inter-mediate, which then results in two structurally-independent minimal-energy crossing points (CIs) towards the syn(C-O) and anti(C-O) sides, respectively. The preference of surface hopping for a certain CI is responsible for the different dynamics of each configuration.