New synchrotron based studies of the photoelectron ionization spectra (PES) for the isomeric 1- and 2-methyltetrazoles (1- and 2-MeTet) show markedly higher resolution than previous reports. The unusual spectral profiles suggest that a considerable overlay of the ionic states occurs for both molecules. Under these circumstances of near degeneracy of two or more ionic states, mutual annihilation of vibrational fine structure occurs for all except the strongest vibrational states; the PES just reflects the resultants rather than full spectra. Theoretical determination of the adiabatic ionization energies (AIEs) proved a challenge; the most successful method was second order Møller-Plesset perturbation theory (MP2). These calculations suggest that the lowest PES bands for both isomers contain ionization both from lone pair σ-orbitals (²A′) on the N-atoms (LP_N) and π-orbitals (²A″). The lowest experimental AIEs are as follows: 1-MeTet is 10.315 eV assigned to 1²A′, while 2-MeTet is 10.543 eV assigned to 1²A″. Franck-Condon analysis shows that the lowest ionization energy regions of both spectra are dominated by IE from the LP_N ²A′ manifold, even though the ²A″ states have a higher absolute intensity. In this example, we have utilized a VUV Rydberg state to assist simplification of the PES; more frequently, the PES assignment is simpler and assists the location of Rydberg states in the VUV. The very slow spectral onset for 2-MeTet demonstrates the importance of vertical ionization energy calculations since maxima are more readily measured than slow onsets. These were performed at the equilibrium structure of the X¹A′ state, using both multi-reference multi-root configuration interaction and the ionization potential variant of the equations-of-motion coupled cluster method, with single and double excitations (EOMIP-CCSD). This enabled the principal ionization bands to be identified over a wider range of energy. Attempts to study the higher ionic states by EOMIP-CCSD showed that several states of each symmetry are close to degenerate for 1-MeTet, in particular. A multi-configuration self-consistent field study confirmed the small separation of ionic states, but state switching during the optimization process largely disabled this method.

中文翻译：

---

异构的1-和2-甲基四唑的光电子能谱；从头算起它们的平衡结构和振动分析

基于新的基于同步加速器的1-甲基和2-甲基四唑异构体（1-和2- MeTet的光电子电离光谱（PES）研究）显示的分辨率明显高于以前的报告。不寻常的光谱曲线表明，两个分子的离子态都有相当大的重叠。在两个或多个离子态几乎简并的这些情况下，除最强的振动态外，所有其他状态都发生了振动精细结构的相互an灭。PES只是反映结果，而不是全谱图。绝热电离能（AIEs）的理论确定证明是一个挑战。最成功的方法是二阶Møller-Plesset微扰理论（MP2）。这些计算表明，两种异构体的最低PES带均包含N原子（LP _N）和π轨道（²）上的孤对σ轨道（² A'）的电离。一个”）。最低实验认证的独立实体如下：1- MeTet是10.315 eV的分配给1个² A'，而2- MeTet是分配给1名10.543 eV的² A“。弗兰克-康登分析表明，这两种谱的最低电离能区由IE从LP主导_Ñ ² A'歧管，即使² A“状态具有较高的绝对强度。在这个例子中，我们利用了VUV Rydberg状态来简化PES。PES分配更加频繁，并且可以简化Rydberg州在VUV中的位置。2- MeTet的光谱起效非常慢证明了垂直电离能计算的重要性，因为最大值比缓慢发作更容易测量。这些是在X ¹ A'状态的平衡结构下进行的，使用多参考多根组态相互作用和运动方程耦合簇方法的电离势变体，具有单激发和双激发（EOMIP-CCSD） ）。这使得可以在更宽的能量范围内识别出主要的电离带。通过EOMIP-CCSD研究更高离子态的尝试表明，对于1- MeTet，每种对称性的几种态都接近于简并， 尤其是。一项多配置自洽现场研究证实了离子态的微小分离，但是在优化过程中进行状态切换在很大程度上禁用了该方法。