硫代苯酮超快开环初期及以后的紫外光化学追踪
Tracking the Ultraviolet Photochemistry of Thiophenone During and Beyond the Initial Ultrafast Ring Opening
摘要：
光致异构化反应，包括开环反应，是自然界许多过程的核心。这种反应的机制是由耦合的电子和核动力学在飞秒尺度上展开的微妙相互作用决定的，然后是能量在不同振动自由度中的缓慢重新分配。在这里，我们应用时间分辨光电子能谱学与种子极紫外自由电子激光跟踪超快开环的气相噻吩分子在265 nm的光激发。当结合尖端的从头算电子结构和分子动力学计算的激发态和基态分子，结果提供了前所未有的见解电子和核动力学的这类基本的反应。初始的开环和非绝热耦合到电子基态示出由弹道SC键扩展驱动，并在350飞秒内完成。理论和实验也允许清晰的可视化丰富的基态动力学，包括形成和相互转换，几个开环异构体和改造的环状结构，和碎片（CO损失）在更长的时间尺度。
英文摘要：
Photoinduced isomerization reactions, including ring-opening reactions, lie at the heart of many processes in nature. The mechanisms of such reactions are determined by a delicate interplay of coupled electronic and nuclear dynamics unfolding on the femtosecond scale, followed by the slower redistribution of energy into different vibrational degrees of freedom. Here we apply time-resolved photoelectron spectroscopy with a seeded extreme ultraviolet free electron laser to trace the ultrafast ring opening of gas phase thiophenone molecules following photoexcitation at 265 nm. When combined with cutting edge ab initio electronic structure and molecular dynamics calculations of both the excited and ground state molecules, the results provide unprecedented insights into both electronic and nuclear dynamics of this fundamental class of reactions. The initial ring opening and non-adiabatic coupling to the electronic ground state is shown to be driven by ballistic SC bond extension and to be complete within 350 femtoseconds. Theory and experiment also allow clear visualization of the rich ground-state dynamics involving formation of, and interconversion between, several ring opened isomers and the reformed cyclic structure, and fragmentation (CO loss) over much longer timescales.
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