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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Nonadiabatic dynamics of uracil: Population split among different decay mechanisms
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Nonadiabatic dynamics of uracil: Population split among different decay mechanisms

机译：尿嘧啶的非绝热动力学：种群在不同衰减机制之间的分裂

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摘要

Nonadiabatic dynamics simulations performed at the state-averaged CASSCF method are reported for uracil. Supporting calculations on stationary points and minima on the crossing seams have been performed at the MR-CISD and CASPT2 levels. The dominant mechanism is characterized by relaxation into the S _2 minimum of ππ* character followed by the relaxation to the S_1 minimum of nπ* character. This mechanism contributes to the slower relaxation with a decay constant larger than 1.5 ps, in good agreement with the long time constants experimentally observed. A minor fraction of trajectories decay to the ground state with a time constant of about 0.7 ps, which should be compared to the experimentally observed short constant. The major part of trajectories decaying with this time constant follows the ππ* channel and hops to the ground state via an ethylenic conical intersection. A contribution of the relaxation proceeding via a ring-opening conical intersection was also observed. The existence of these two latter channels together with a reduced long time constant is responsible for a significantly shorter lifetime of uracil compared to that of thymine.
机译：报告了尿嘧啶在状态平均CASSCF方法下进行的非绝热动力学模拟。已经在MR-CISD和CASPT2级别上对固定点和交叉接缝上的最小值进行了支持性计算。主导机制的特征在于松弛到ππ*字符的S _2最小值，然后松弛到ππ*字符的S_1最小值。这种机制有助于衰减较慢，衰减常数大于1.5 ps，这与实验观察到的长时间常数非常吻合。轨迹的一小部分以约0.7 ps的时间常数衰减至基态，应将其与实验观察到的短常数进行比较。随该时间常数衰减的轨迹的主要部分遵循ππ*通道，并通过烯属圆锥形交点跳至基态。还观察到通过开环圆锥形相交进行的松弛过程的贡献。与胸腺嘧啶相比，后两个通道的存在以及降低的长时间常数使尿嘧啶的寿命显着缩短。

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