Nonadiabatic Dynamics of Uracil: Population Split among Different Decay Mechanisms
Nonadiabatic Dynamics of Uracil: Population Split among Different Decay Mechanisms
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DOI：
10.1021/jp201327w
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发表时间：
2011-06-02
影响因子：
2.9
通讯作者：
Lischka, Hans
中科院分区：
文献类型：
--
作者：
Nachtigallova, Dana;Aquino, Adelia J. A.;Lischka, Hans
采用状态平均CASSCF方法对尿嘧啶进行了非绝热动力学模拟。在MR-CISD和CASPT 2水平上对交叉接缝上的固定点和最小值进行了支持计算。主要机制的特征在于松弛到S（2）最小值的pi pi* 字符，随后松弛到S（1）最小值的n pi* 字符。这种机制有助于较慢的弛豫与衰减常数大于1.5 ps，在很好的协议与实验观察到的长时间常数。一小部分的轨迹衰减到基态的时间常数约为0.7 Ps，这应该是比较实验观察到的短常数。随时间常数衰减的轨道的主要部分遵循π π * 通道，并通过烯属圆锥交叉点跳到基态。还观察到通过开环圆锥相交的松弛过程的贡献。后两种通道的存在以及降低的长时间常数导致尿嘧啶的寿命显著短于胸腺嘧啶。
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 pi pi* character followed by the relaxation to the S(1) minimum of n pi* 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 pi pi* 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.