胞嘧啶酮和烯醇互变异构体的单重态和三重态激发态动力学研究
A singlet and triplet excited-state dynamics study of the keto and enol tautomers of cytosine
摘要：
为了了解分子束飞秒泵浦-探测光电离光谱实验的结果，采用从头算表面跳跃方法研究了胞嘧啶酮和烯醇形式的光诱导激发态动力学。单重态和三重态都包括在动力学中。结果表明，三重态对酮式互变异构体的弛豫起重要作用，而对烯醇式互变异构体的弛豫作用较小。在这两种形式中，发现T $_1$状态最小值的能量太低，在标准光电离光谱实验中无法检测到，因此实验衰减时间应该从同时弛豫到基态和额外的系间交叉，然后内部转换到T $_1$状态。在协议与现有的实验寿命，我们观察到三个衰减常数7 fs，270 fs和1900 fs -前两个来自酮互变异构体和较长的一个从烯醇互变异构体。烯醇形式的失活是由于通过两个烯属类型的S $_1$ /S $_0$锥形交叉点内部转化为基态。
英文摘要：
The photoinduced excited-state dynamics of the keto and enol forms of cytosine is investigated using ab initio surface hopping in order to understand the outcome of molecular beam femtosecond pump-probe photoionization spectroscopy experiments. Both singlet and triplet states are included in the dynamics. The results show that triplet states play a significant role in the relaxation of the keto tautomer, while they are less important in the enol tautomer. In both forms, the T$_1$ state minimum is found too low in energy to be detected in standard photoionization spectroscopy experiments and therefore experimental decay times should arise from a simultaneous relaxation to the ground state and additional intersystem crossing followed by internal conversion to the T$_1$ state. In agreement with available experimental lifetimes, we observe three decay constants of 7 fs, 270 fs and 1900 fs - the first two coming from the keto tautomer and the longer one from the enol tautomer. Deactivation of the enol form is due to internal conversion to the ground state via two S$_1$/S$_0$ conical intersections of ethylenic type.
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