Zhang Juanjuan, Peng Jiawei, Hu Deping, Lan Zhenggang
SCNU Environmental Research Institute, Guangdong Provincial Key Laboratory of Chemical Pollution and Environmental Safety & MOE Key Laboratory of Environmental Theoretical Chemistry, South China Normal University, Guangzhou 510006, China.
School of Environment, South China Normal University, Guangzhou 510006, China.
Phys Chem Chem Phys. 2021 Nov 24;23(45):25597-25611. doi: 10.1039/d1cp03226g.
The photolysis mechanism of methyl nitrate (CHONO) was studied using the on-the-fly surface hopping dynamics at the XMS-CASPT2 level. Several critical geometries, including electronic state minima and conical intersections, were obtained, which play essential roles in the nonadiabatic dynamics of CHONO. The ultrafast nonadiabatic decay dynamics to the ground state were simulated, which gives a proper explanation on the broad and structureless absorption spectra of CHONO. The photodissociation channels, including CHO + NO, CHO + NO + O, and others, as well as their branching ratios, were identified. When the dynamics starts from the lowest two electronic states (S and S), the CHO + NO channel is the dominant photolysis pathway, although we observed the minor contributions of other channels. In contrast, when the trajectories start from the third excited state S, both CHO + NO and CHO + NO + O channels become important. Here the CHO-NO bond dissociation takes place first, and then for some trajectories, the N-O bond of the NO part breaks successively. The quasi-degeneracy of electronic states may exist in the dissociation limits of both CHO + NO and CHO + NO + O channels. The current work provides valuable information in the understanding of experimental findings of the wavelength-dependent photolysis mechanism of CHONO.
采用XMS-CASPT2水平的即时表面跳跃动力学研究了硝酸甲酯（CH₃ONO₂）的光解机理。获得了几个关键几何结构，包括电子态极小值和锥形交叉点，它们在CH₃ONO₂的非绝热动力学中起着至关重要的作用。模拟了到基态的超快非绝热衰减动力学，这对CH₃ONO₂的宽且无结构的吸收光谱给出了合理的解释。确定了光解离通道，包括CHO + NO、CHO + NO + O等及其分支比。当动力学从最低的两个电子态（S₀和S₁）开始时，CHO + NO通道是主要的光解途径，尽管我们观察到其他通道的贡献较小。相比之下，当轨迹从第三激发态S₂开始时，CHO + NO和CHO + NO + O通道都变得重要。这里CHO-NO键首先发生解离，然后对于一些轨迹，NO部分的N-O键相继断裂。CHO + NO和CHO + NO + O通道的解离极限中可能存在电子态的准简并性。目前的工作为理解CH₃ONO₂波长依赖的光解机理的实验结果提供了有价值的信息。
