C8和C12碳环有趣的电子结构
Intriguing Electronic Structures of C8 and C12 Carbon Rings
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中文总结 AI 辅助
研究C8和C12碳环的电子结构，分析从多炔到累积烯结构转变时电子结构变化及洪德规则违反原因，研究低能态弛豫路径，揭示第一单重激发态和最低能量累积烯态在不同结构下的特性。
中文摘要 AI 辅助
我们报告了基态和众多激发电子态。在基态下，C4n环是具有多炔结构的闭壳层体系，可归类为双反芳香分子。在其能量最低的三重态，环呈现芳香性累积烯结构。从多炔结构到累积烯结构的适度几何变化会使电子结构发生显著改变，如在C8和C12的累积烯结构中洪德规则被违反。分析了违反原因，研究了C8从多炔到累积烯几何结构转变的低能态弛豫路径，其第一单重激发态在多炔结构中为开壳层，在累积烯结构中为闭壳层，能量最低的累积烯态是开壳层单重态，会弛豫到闭壳层多炔基态。
英文摘要
We report on the ground and numerous excited electronic states. In the ground state the C4n rings are closed-shell systems possessing polyynic structures and can be classified as double anti-aromatic molecules. In their energetically lowest lying triplet state the rings exhibit aromatic cumulenic structures. The overall change in the electronic structures is rather dramatic upon the found moderate geometric changes from polyynic to cumulenic structure. Among others, Hund's rule is violated in both C8 and C12 in their cumulenic structures. We mention that until now, graphene is the only carbon allotrope reported to violate Hund's rule. The reasons for the violation are analyzed. Much effort has been invested to understand the relaxation pathways of the low-lying states leading the C8 from polyynic to cumulenic geometry and vice versa. On its minimum energy path, the first singlet excited state changes from open-shell character in the polyynic structure to a closed-shell state in the cumulenic structure. The cumulenic state lowest in energy is an open-shell singlet which relaxes to the closed-shell polyynic ground state.
