Daresbury Laboratory, Daresbury, Warrington, Cheshire WA4 4AD, United Kingdom.
School of Chemistry, University of Nottingham, Nottingham NG7 2RD, United Kingdom.
J Chem Phys. 2017 Oct 28;147(16):164307. doi: 10.1063/1.4999433.
The valence shell photoelectron spectra of 2-chloropyridine and 3-chloropyridine have been studied both experimentally and theoretically. Synchrotron radiation has been employed to record angle resolved photoelectron spectra in the photon energy range 20-100 eV, and these have enabled anisotropy parameters and branching ratios to be derived. The experimental results have been compared with theoretical predictions obtained using the continuum multiple scattering Xα approach. This comparison shows that the anisotropy parameter associated with the nominally chlorine lone-pair orbital lying in the molecular plane is strongly affected by the atomic Cooper minimum. In contrast, the photoionization dynamics of the second lone-pair orbital, orientated perpendicular to the molecular plane, seem relatively unaffected by this atomic phenomenon. The outer valence ionization has been studied theoretically using the third-order algebraic-diagrammatic construction (ADC(3)) approximation scheme for the one-particle Green's function, the outer valence Green's function method, and the equation-of-motion (EOM) coupled cluster (CC) theory at the level of the EOM-IP-CCSD and EOM-EE-CC3 models. The convergence of the results to the complete basis set limit has been investigated. The ADC(3) method has been employed to compute the complete valence shell ionization spectra of 2-chloropyridine and 3-chloropyridine. The relaxation mechanism for ionization of the nitrogen σ-type lone-pair orbital (σ) has been found to be different to that for the corresponding chlorine lone-pair (σ). For the σ orbital, π-π* excitations play the main role in the screening of the lone-pair hole. In contrast, excitations localized at the chlorine site involving the chlorine π lone-pair and the Cl 4p Rydberg orbital are the most important for the σ orbital. The calculated photoelectron spectra have allowed assignments to be proposed for most of the structure observed in the experimental spectra. The theoretical work also highlights the formation of satellite states, due to the breakdown of the single particle model of ionization, in the inner valence region.
2-氯吡啶和 3-氯吡啶的价层光电子能谱已通过实验和理论进行了研究。同步辐射被用来记录光子能量范围为 20-100 eV 的角分辨光电子能谱，由此可以推导出各向异性参数和分支比。实验结果与使用连续多次散射 Xα方法获得的理论预测进行了比较。该比较表明，与分子平面中名义上的氯孤对轨道相关的各向异性参数强烈受到原子 Cooper 最小值的影响。相比之下，垂直于分子平面取向的第二孤对轨道的光致电离动力学似乎相对不受这种原子现象的影响。使用单粒子格林函数的三阶代数图论构造（ADC(3)）近似方案、外价格林函数方法和运动方程（EOM）耦合簇（CC）理论（EOM-IP-CCSD 和 EOM-EE-CC3 模型），对外部价层的光致电离进行了理论研究。已经研究了结果收敛到完全基组极限的情况。ADC(3)方法被用于计算 2-氯吡啶和 3-氯吡啶的完整价层光电子能谱。氮σ型孤对轨道（σ）的电离弛豫机制与相应的氯孤对（σ）的弛豫机制不同。对于σ轨道，π-π*激发在屏蔽孤对空穴方面起着主要作用。相比之下，涉及氯π孤对和 Cl 4p Rydberg 轨道的氯位点局部激发对于σ轨道是最重要的。计算的光电子能谱允许对实验光谱中观察到的大多数结构进行分配。理论工作还强调了由于内壳层区域中电离的单粒子模型的破坏而形成卫星态。
