羰基化合物激发态势能面交叉动力学的共振拉曼光谱和CASSCF计算研究

The dynamics of the excited state potential energy surface (PES) crossing plays an important role in the photochemical reactions. In the vicinity of a conical intersection in the Franck-Condon region, the internal conversion (IC) process is extremely fast so that it is difficult to detect directly by current ultrafast spectroscopic techniques. In this proposal, the resonance Raman spectroscopic in conjunction with CASSCF computational method is employed to study the excited state PES crossing dynamics of the carbonyl compounds. Through extensive study of the selected molecule systems including unsaturated aldehydes (ketones), nucleobases, and aromatic aldehydes (ketones), we expect to discover the characteristic coordinates (Raman marks) that label the dynamics of the conical intersection between the interested PES, and to reveal the regularities in the influences of the substituents and the solvents on the excited state PES crossing dynamics in the Franck-Condon region of nucleobases. We explore the regularities in the effect of the substituent-induced excited state intramolecular proton-transfer and electron transfer reaction channels on the FC region conical intersectional dynamics of the carbonyl coumpounds. Based on the exploratory research on the excited state structural dynamics of the carbonyl compounds through the use of matrix-isolation combined resonance Raman technique under cryogenic condition, we aim to reveal the mechanism that solvents affect the PES crossing dynamics of carbonyl compounds in the Franck-Condon region on the molecular-level. Our studies will provide a unique way in the investigation of the PES crossing dynamics in the photochemistry.

激发态势能面交叉动力学在光化学反应中起着举足轻重的作用。Franck-Condon(FC)区域势能面锥形交叉点附近的内转换过程极其快速，现有超快实验技术难以直接观测。本项目采用共振拉曼光谱技术和CASSCF等计算方法，开展羰基化合物激发态势能面锥形交叉动力学研究。期望通过不饱和烯醛(酮)、核酸碱基、芳香醛(酮)及其衍生物等一系列分子体系的研究，找到与各类势能面锥形交叉动力学相关的特征反应坐标(拉曼标记)，探明羰基化合物FC区域各类势能面交叉动力学的取代基效应和溶剂效应规律。探索不同取代基(NH2、CN等)引发激发态分子内质子转移和电荷转移反应通道对FC区域势能面锥形交叉通道的调控途径。采用低温基质隔离-共振拉曼光谱技术，研究基质隔离条件下羰基化合物激发态结构动力学，发现溶剂性质影响羰基化合物FC区域势能面交叉动力学的微观机制。本研究将为势能面交叉动力学研究提供一条独途径。

激发态势能面交叉动力学在光化学反应中起着举足轻重的作用。Franck-Condon区域势能面交叉点附近的内转换过程极其快速，现有超快实验技术难以直接观测。本项目采用共振拉曼光谱技术和CASSCF等计算方法，开展羰基化合物激发态势能面锥形交叉动力学研究。开展了环己烯酮、开链共轭烯酮、嘧啶碱基、吡啶酮、芳香醛（酮）等一系列分子体系振动光谱测量和CASSCF计算，指认了振动光谱和电子光谱，获得了单重激发态/激发三重态以及相关势能面交叉点的优化几何结构和能量信息；开展了共振拉曼光谱指认和绝对拉曼横截面的量子波包理论计算拟合，获得了无量纲简正模位移量和光谱展宽参数，揭示了激发态势能面交叉动力学和弛豫机理。发现了共振拉曼光谱强度模式与势能面交叉点结构的关系，探明了羰基化合物共振拉曼光谱强度模式随取代基和溶剂变化的动力学机制，提出了共振拉曼散射的瞬间极化模型，赋予了Kramers-Heisenberg共振拉曼散射理论和Herzberg-Teller振动电子耦合理论新的内涵。设计和搭建了低温基质隔离-共振拉曼光谱实验装置，为分子激发态势能面交叉动力学研究和拉曼非一致性（溶剂）效应的研究提供了新的工具。