A direct dynamics study of the exotic photochemistry of the simplest Criegee intermediate, CH2OO.
A direct dynamics study of the exotic photochemistry of the simplest Criegee intermediate, CH2OO.
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对最简单的 Criegee 中间体 CH2OO 的奇异光化学的直接动力学研究。
DOI：
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发表时间：
2022
期刊：
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通讯作者：
Tolga N. V. Karsili
中科院分区：
文献类型：
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作者：
Ernest Antwi;R. Bush;Barbara Marchetti;Tolga N. V. Karsili
克里基中间体是现代化学中最迷人的分子之一。它们是高度活跃的中间体，在从大气化学到有机合成的各个领域都发挥着重要作用。它们的激发态化学是奇特而复杂的，无数的电子态可以促进它们的光解动力学。本文报道了一项多态直接动力学（全维）研究，利用最先进的MS-CASPT2轨道表面跳变技术，对最简单的Criegee中间体ch220的光致破碎进行了研究。在垂直激发到强吸收的S2（1ππ*）态后，观察到分离的O + CH2O碎片的母电子态之间的内部转换，从而观察到分离的电子态特征的变化，传统上，这可能被视为势能面的经典渐近区域。我们认为，这种远距离的内部转换可能解释了在CH2O光激发后观察到的O(1D) + CH2O（S0）产物中不寻常的和非直观的总动能分布。本研究结果还揭示了七个单重态电子与解离之间的相互作用，从而产生实验观察到的O(1D) + CH2O（S0）和O(3P) + CH2O（T1）产物。前者（单线态）产物更受青睐，分支比约为80%，量化了迄今为止在速度图成像实验中观察到的未知产物分支比。据我们所知，在经典的渐近分离中，这种导致来自共同亲本的片段对的电子态特征变化的远距离内部转换迄今尚未在分子光解的情况下被认识到。
Criegee intermediates are amongst the most fascinating molecules in modern-day chemistry. They are highly reactive intermediates that find vital roles that range from atmospheric chemistry to organic synthesis. Their excited state chemistry is exotic and complicated, and a myriad of electronic states can contribute to their photodissociation dynamics. This article reports a multi-state direct dynamics (full-dimensional) study of the photoinduced fragmentation of the simplest Criegee intermediate, CH2OO, using state-of-the-art MS-CASPT2 trajectory surface hopping. Following vertical excitation to the strongly absorbing S2(1ππ*) state, internal conversion, and thus changes in the electronic state character of the separating O + CH2O fragments, is observed between parent electronic states at separations that, traditionally, might be viewed as the classically asymptotic region of the potential energy surface. We suggest that such long-range internal conversion may account for the unusual and non-intuitive total kinetic energy distribution in the O(1D) + CH2O(S0) products observed following photoexcitation of CH2OO. The present results also reveal the interplay between seven singlet electronic states and dissociation to yield the experimentally observed O(1D) + CH2O(S0) and O(3P) + CH2O(T1) products. The former (singlet) products are favored, with a branching ratio of ca. 80%, quantifying the hitherto unknown product branching ratios observed in velocity map imaging experiments. To the best of our knowledge, such long-range internal conversions that lead to changes in the electronic state character of the fragment pairs originating from a common parent - at classically asymptotic separations - have not been recognized hitherto in the case of a molecular photodissociation.