胸腺嘧啶中意外的氢解离：来自一种新型耦合簇理论的预测
Unexpected hydrogen dissociation in thymine: predictions from a novel coupled cluster theory
AI总结：
本研究采用新型耦合簇方法模拟胸腺嘧啶超快动力学，证实了$ππ^*$到$nπ^*$的超快跃迁，还预测了一条可导致氢解离的$πσ^*$光化学通道，为相关实验研究提供了新方向。
摘要：
过去三十年间，胸腺嘧啶在紫外线辐射激发下的演化过程一直是热议的研究主题。目前学界普遍认为，其超快激发态衰减源于亮$ππ^*$态到暗$nπ^*$态的无辐射跃迁。然而，相互矛盾的理论预测使得实验数据难以解读。本研究采用迄今最高水平的理论方法模拟胸腺嘧啶中的超快动力学，利用一种新的耦合簇方法开展波包动力学计算。模拟结果证实了超快的$ππ^*$到$nπ^*$跃迁（$τ = 41 \pm 14$ fs）。此外，预测得到的氧边X射线吸收光谱与实验结果在定量层面吻合。模拟还预测了一条尚未被表征的光化学途径：一条$πσ^*$通道，可导致胸腺嘧啶中两个N-H键之一发生氢解离。类似的行为已在包括腺嘌呤在内的其他杂芳族化合物中被发现，已有多位学者推测胸腺嘧啶中可能存在类似途径，但这一点从未在理论或实验上得到证实。该预测呼吁研究人员开展新的实验工作，以确认或排除该通道的存在。
英文摘要：
The fate of thymine upon excitation by ultraviolet radiation has been the subject of intense debate over the past three decades. Today, it is widely believed that its ultrafast excited state decay stems from a radiationless transition from the bright $ππ^*$ state to a dark $nπ^*$ state. However, conflicting theoretical predictions have made the experimental data difficult to interpret. Here we simulate the ultrafast dynamics in thymine at the highest level of theory to date, performing wavepacket dynamics with a new coupled cluster method. Our simulation confirms an ultrafast $ππ^*$ to $nπ^*$ transition ($τ = 41 \pm 14$ fs). Furthermore, the predicted oxygen-edge X-ray absorption spectra agree quantitatively with the experimental results. Our simulation also predicts an as-yet uncharacterized photochemical pathway: a $πσ^*$ channel that leads to hydrogen dissociation at one of the two N-H bonds in thymine. Similar behavior has been identified in other heteroaromatic compounds, including adenine, and several authors have speculated that a similar pathway may exist in thymine. However, this was never confirmed theoretically or experimentally. This prediction calls for renewed efforts to experimentally identify or exclude the presence of this channel.
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