1，3-环己二烯的光化学开环反应：反应态的复杂动力学演化
The photochemical ring-opening reaction of 1,3-cyclohexadiene: complex dynamical evolution of the reactive state
摘要：
光化学诱导的1，3-环己二烯（CHD）到1，3，5-己三烯（HT）的开环异构化反应是周环反应的教科书例子，并且已经用先进的光谱技术进行了充分的研究。普遍接受的异构化途径的描述开始于价激发到最低的亮态，然后通过锥形交叉点到达暗的双激发态，最后在返回环状分子的基态或导致开链异构体的实际开环反应之间分支。传统上认为，在Franck-Condon几何条件下，暗反应态对应于CHD的第二激发态。在这里，在一个联合的实验和计算的努力，我们证明了激发-去激发过程的演变是比通常描述的复杂得多。特别是，我们表明，一个最初的高躺电子态沿反应路径的能量平稳下降起着关键作用的开环反应。我们工作的概念基础是，这里要考虑的动力学是由非绝热态决定的，非绝热态的布居是与观察到的光电子信号密切相关的。
英文摘要：
The photochemically induced ring-opening isomerization reaction of 1,3-cyclohexadiene (CHD) to 1,3,5-hexatriene (HT) is a textbook example of a pericyclic reaction, and has been amply investigated with advanced spectroscopic techniques. The generally accepted description of the isomerization pathway starts with a valence excitation to the lowest-lying bright state, followed by a passage through a conical intersection to a dark doubly excited state, and finally a branching between either the return to the ground state of the cyclic molecule or the actual ring-opening reaction leading to the open-chain isomer. It was traditionally assumed that the dark reactive state corresponds to the second excited state of CHD at the Franck-Condon geometry. Here in a joint experimental and computational effort we demonstrate that the evolution of the excitation-deexcitation process is much more complex than usually described. In particular, we show that an initially high-lying electronic state smoothly decreasing in energy along the reaction path plays a key role in the ring-opening reaction. The conceptual basis of our work is that the dynamics to consider here is determined by diabatic states, whose populations are the ones closely related to the observed photoelectron signal.
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