Ultrafast photodissociation dynamics of 2-ethylpyrrole: adding insight to experiment with ab initio multiple cloning.
Ultrafast photodissociation dynamics of 2-ethylpyrrole: adding insight to experiment with ab initio multiple cloning.
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2-乙基吡咯的超快光解离动力学：为从头多重克隆实验增添见解。
DOI：
10.1039/c8cp06359a
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发表时间：
2019
期刊：
影响因子：
--
通讯作者：
Green JA
中科院分区：
文献类型：
--
作者：
Green JA
用从头算多克隆方法对2-乙基吡咯(2-EP)在S_1和S_2πσ*态上的超快光解动力学进行了全量子模拟。AIMC用精确的电子结构方法“在飞行中”处理电子，用波函数通过Ehrenfest轨迹制导的高斯波包的基本集处理核动力学。得到了总动能释放(TKER)谱、速度图图像和N-H离解时间。将这些结果与时间分辨速度图成像研究的结果进行了比较，AIMC方法能够提供实验数据的定量再现，包括50-80fs的解离时间。对解离机理有了新的认识，实验测得的时间常数由两个组分组成。首先，2-EP分子在<；50fs有贡献，这些分子在N-H伸展坐标中有足够的能量几乎立即越过势垒解离，紧随其后的是2-EP分子的第二个较慢的贡献，在找到绕过势垒解离的方法之前，必须对势能面进行采样。由于激光脉冲的时间宽度遮挡了50ps窗口内的动力学，实验上没有观察到这种两组分机制，并首次从理论上证明了这一机制。对选择性的2-EP进行了计算，证明了AIMC能够对解离时间常数产生动力学同位素效应，并正确地预测了tker谱中向低能量方向的移动。S2的πσ*态相对于S1的πσ*态也是不稳定的，当初始激发到S2时，N-H解离沿着S1进行。这项工作表明，最先进的理论和实验的结合可以为N-H解离机理提供前所未有的新见解，并具有更广泛的杂原子氢键解离的诱人前景。
The ultrafast photodissociation dynamics of 2-ethylpyrrole (2-EP) is simulated in a fully quantum manner on the S1 and S2 πσ* states by the ab initio multiple cloning (AIMC) method. AIMC treats electrons with accurate electronic structure methods “on the fly”, and nuclear dynamics with wavefunction propagation via a basis set of Ehrenfest trajectory guided Gaussian wavepackets. Total kinetic energy release (TKER) spectra are produced, as well as velocity map images and N–H dissociation times. These are compared to results from time-resolved velocity map imaging studies, and the AIMC method is able to provide quantitative reproduction of experimental data, including dissociation times of 50–80 fs. Novel insight into the dissociation mechanism is then obtained, with the experimentally obtained time constant shown to be composed of two components. Firstly, there is a contribution in <50 fs from 2-EP molecules that have sufficient energy in the N–H stretch coordinate to dissociate almost immediately over the barrier, and this is followed by a second slower contribution from 2-EP molecules that must sample the potential energy surface before finding a way around the barrier to dissociate. This two component mechanism is not observed experimentally due to the temporal widths of the laser pulses obscuring the dynamics in the <50 fs window, and is shown for the first time via theory. Calculations are also performed on selectively deuterated 2-EP, demonstrating that AIMC is able to produce a kinetic isotope effect for the dissociation time constant, and correctly predict a shift to lower energy in the TKER spectrum. The S2 πσ* state is also shown to be unstable with respect to the S1 πσ* state, with the N–H dissociation proceeding along S1 when initially excited to S2. This work demonstrates that the combination of state of the art theory and experiments can provide unprecedented novel insight into the N–H dissociation mechanism, with the tantalising prospect of providing insight into more general heteroatom hydride bond dissociation.
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影响因子：
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作者：
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