Department of Chemistry, Oregon State University, Corvallis, Oregon 97331-4003, United States.
J Phys Chem A. 2012 Jul 5;116(26):7016-22. doi: 10.1021/jp303323e. Epub 2012 Jun 22.
We report the electronic and vibrational spectroscopy of chrysene using resonantly enhanced multiphoton ionization (REMPI) and zero kinetic energy (ZEKE) photoelectron spectroscopy. As an isomer of tetracene, chrysene contains a kink in the middle of the four fused hexagonal rings, which complicates not just the symmetry but, more importantly, the molecular orbitals and hence vibronic transitions. Incidentally, the two nearby electronically excited states of chrysene have the same symmetry, and vibronic coupling introduces no out-of-plane vibrational modes. As a result, the REMPI spectrum of chrysene contains essentially only in-plane ring deformation modes, similar to that of tetracene. However, density functional calculations using gaussian even after the inclusion of vibronic coupling can only duplicate the observed REMPI spectrum in a qualitative sense, and the agreement is considerably worse than our recent work on a few pericondensed polycyclic aromatic hydrocarbons and on tetracene. The ZEKE spectrum of chrysene via the origin band of the intermediate electronic state S(1), however, can be qualitatively reproduced by a straightforward Franck-Condon calculation. The ZEKE spectra from vibrationally excited states of the S(1), on the other hand, demonstrate some degree of mode selectivity: the overall intensity of the ZEKE spectrum can vary by an order of magnitude depending on the vibrational mode of the intermediate state. A scaling factor in the theoretical vibrational frequency for the cation is also needed to compare with the experimental result, unlike tetracene and pentacene.
我们报告了使用共振增强多光子电离（REMPI）和零动能（ZEKE）光电子能谱研究 Chrysene 的电子和振动光谱。作为四环的异构体，Chrysene 中间的四个融合的六元环有一个拐点，这不仅使对称性变得复杂，更重要的是，使分子轨道和振动态发生变化。顺便说一下，Chrysene 的两个相邻的电子激发态具有相同的对称性，振动态耦合不会引入非平面振动模式。因此，Chrysene 的 REMPI 光谱基本上只包含平面环变形模式，类似于四环的光谱。然而，使用高斯的密度泛函计算，即使包含了振动态耦合，也只能定性地复制观察到的 REMPI 光谱，其吻合度远不如我们最近对一些稠合多环芳烃和四环的研究。然而，通过中间电子态 S(1)的起始带获得的 Chrysene 的 ZEKE 光谱可以通过直接的 Franck-Condon 计算定性地再现。另一方面，S(1)的振动激发态的 ZEKE 光谱表现出一定程度的模式选择性：ZEKE 光谱的整体强度可以根据中间态的振动模式变化一个数量级。与四环和五环不同，还需要对阳离子的理论振动频率进行缩放因子调整，以与实验结果进行比较。
