Reaction path of a sub-200 fs photochemical electrocyclic reaction
Reaction path of a sub-200 fs photochemical electrocyclic reaction
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DOI：
10.1021/jp010359p
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发表时间：
2001-05-10
影响因子：
2.9
通讯作者：
Fuss, W
中科院分区：
文献类型：
--
作者：
Garavelli, M;Page, CS;Fuss, W
用从头算多态二阶微扰理论(MS-CASPT2)计算了环己二烯(CHD)的超快光化学电环开环反应路径：这条路径是沿着一个复杂的反应坐标演化的，跨越两个无势垒激发态势能面，最终导致通过S-1/S-0锥形交点失活。观察到的激发态动力学包括三个连续的相，其寿命(旅行时间)分别为10、43和77飞秒。在这项工作中，我们将每个阶段与CHD分子结构沿不同模式的演变联系起来。特别地，我们证明了：(A)CHD从光谱(1B(2))态到较低的暗(2A(1))激发态的衰变涉及沿着对应于键扩展和对称破缺骨架弯曲的混合的高度弯曲坐标的运动，(B)在2A(1)(S-1)态和发现的2A(1)-->；1A(1)(即，S-1->；S-0)衰变涉及沿相同的不对称弯曲模式的大幅度位移，最终导致S-1/S-0锥形交点，以及(C)应用一种新的策略来映射多维S-1/S-0交点空间，表明2A(1)激发态的超短77fs寿命是由于跨越2A(1)能面低位部分的一组广泛的圆锥交点的存在。(A)和(B)点通过讨论先前报道的和新的关于CHD和两个二烷基衍生物α-松油烯和α-水芹烯的飞秒时间分辨光谱数据的结果来验证。并从驱动力的角度给出了解释。
Ab initio multistate second-order perturbation theory (MS-CASPT2) calculations are used to map the reaction path for the ultrafast photochemical electrocyclic ring-opening of cyclohexa-1,3-diene (CHD): This path is characterized by evolution along a complex reaction coordinate extending over two barrierless excited state potential energy surfaces and ultimately leading to deactivation through a S-1/S-0 conical intersection. The observed excited-state dynamics involve three sequential phases with lifetimes (traveling times) of 10, 43, and 77 fs, respectively. In this work we associate each phase to the evolution of the CHD molecular structure along a different mode. In particular, we show that (a) the decay of CHD from its spectroscopic (1B(2)) state to a lower lying dark (2A(1)) excited state involves motion along a highly curved coordinate corresponding to a mixture of a bond expansion and symmetry breaking skeletal bending, (b) the evolution pn the 2A(1) (S-1) state and the find 2A(1)--> 1A(1) (i.e., S-1-->S-0) decay involve a large amplitude displacement along the same asymmetric bending mode which ultimately leads to a S-1/S-0 conical intersection, and (c) the application of a novel strategy for mapping the multidimensional S-1/S-0 intersection space indicates that the ultrashort 77 fs Lifetime of the 2A(1) excited state is due to the existence of an extensive set of S-1/S-0 conical intersection points spanning the low-lying part of the 2A(1) energy surface. Points (a) and (b) are validated by discussing the results of previously reported and new femtosecond time-resolved spectroscopic data on CHD and on the two dialkyl derivatives alpha -terpinene and alpha -phellandrene. An interpretation in terms of driving forces is also given.