期刊
PHYSICAL CHEMISTRY CHEMICAL PHYSICS
卷 24, 期 27, 页码 16724-16731出版社
ROYAL SOC CHEMISTRY
DOI: 10.1039/d2cp01860h
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资金
- National Science Foundation [2003422]
- Direct For Mathematical & Physical Scien
- Division Of Chemistry [2003422] Funding Source: National Science Foundation
Criegee intermediates, highly reactive molecules with vital roles in various fields, were studied using state-of-the-art techniques. The study revealed the impact of long-range internal conversion on the products of photoinduced fragmentation.
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 S-2((1)pi pi*) 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(D-1) + CH2O(S-0) 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(D-1) + CH2O(S-0) and O(P-3) + CH2O(T-1) 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.
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