Yamazaki Masakazu, Kishimoto Naoki, Ohno Koichi
Department of Chemistry, Graduate School of Science, Tohoku University, Aramaki, Aoba-ku, Sendai, Japan.
J Phys Chem A. 2006 Jun 8;110(22):7097-104. doi: 10.1021/jp061573m.
Anisotropic interactions between a metastable He(2(3)S) atom and aromatic heterocyclic compounds (thiazole and benzothiazole) as well as their electronic structures were studied by means of collision-energy/electron-energy resolved two-dimensional Penning ionization electron spectroscopy combined with ab initio molecular orbital calculations. Different collision-energy dependence of partial ionization cross sections (CEDPICS) were clearly observed for different ionic states depending on anisotropic extents of molecular orbitals from which an electron is removed. It was found that thiazole and benzothiazole most strongly attract a He(2(3)S) atom around the region where the nitrogen lone pair orbital extends. For another heteroatom, sulfur, it is relatively weak, but a certain attractive interaction was found for the directions perpendicular to the molecular plane. Benzothiazole was shown to widely attract a He(2(3)S) atom in the out-of-plane directions, since the benzene moiety showed a deeper potential well than the five-membered ring. Assignments of the ionic states including shake-up states were also discussed from observed CEDPICS and ab initio molecular orbital calculations. In particular, for the satellite bands, a negative collision energy dependence of the band intensity was well supported by a configuration-interaction calculation that assigns the satellite bands to be the ionization from pi orbitals accompanying pi-pi or n-pi excitations.
通过碰撞能量/电子能量分辨二维潘宁电离电子能谱结合从头算分子轨道计算，研究了亚稳态He(2(3)S)原子与芳香族杂环化合物（噻唑和苯并噻唑）之间的各向异性相互作用及其电子结构。对于不同的离子态，根据电子被移除的分子轨道的各向异性程度，清楚地观察到了部分电离截面的不同碰撞能量依赖性（CEDPICS）。结果发现，噻唑和苯并噻唑在氮孤对轨道延伸的区域周围对He(2(3)S)原子具有最强的吸引力。对于另一个杂原子硫，吸引力相对较弱，但在垂直于分子平面的方向上发现了一定的吸引相互作用。由于苯部分显示出比五元环更深的势阱，苯并噻唑在平面外方向上对He(2(3)S)原子具有广泛的吸引力。还根据观察到的CEDPICS和从头算分子轨道计算讨论了包括振激态在内的离子态归属。特别是对于卫星带，通过将卫星带归属于伴随π-π或n-π激发的π轨道电离的组态相互作用计算，很好地支持了带强度的负碰撞能量依赖性。
