Department of Chemistry, Oregon State University, Corvallis, Oregon 97331-4003, United States.
J Phys Chem A. 2012 Feb 16;116(6):1551-7. doi: 10.1021/jp2109576. Epub 2012 Feb 3.
We report zero kinetic energy (ZEKE) photoelectron spectroscopy of benzo[g,h,i]perylene (BghiP) via resonantly enhanced multiphoton ionization (REMPI). Our analysis concentrates on the vibrational modes of both the first electronically excited state and the ground cationic state. Extensive vibronic coupling due to a nearby electronically excited state manifests through strong Franck-Condon (FC) forbidden bands, which are stronger than even the FC allowed bands in the REMPI spectrum. Theoretical calculations using Gaussian are problematic in identifying the electronic configurations of the excited electronic states and predicting the transition energies. However, by setting the keyword for the second excited electronic state, both density functional theory and configuration interaction methods can reproduce the observed spectrum qualitatively. The general agreement significantly helps with the vibrational assignment. The ZEKE spectra demonstrate propensity in preserving the vibrational excitation of the intermediate electronic state. In addition, almost all ZEKE spectra exhibit a similar vibrational distribution, and the distribution can be reproduced by an FC calculation from the vibronic origin of the first excited electronic state to the cationic state using Gaussian 09. These results suggest a remarkable structural stability of BghiP in accommodating the additional charge. All observed vibrational bands of the cation are IR active, establishing the role of ZEKE spectroscopy in mapping out far-infrared bands for astrophysical applications.
我们通过共振增强多光子电离（REMPI）报告了苯并[g,h,i]苝（BghiP）的零动能（ZEKE）光电子能谱。我们的分析集中在第一电子激发态和基态阳离子的振动模式上。由于附近的电子激发态引起的广泛的振子耦合表现为强 Franck-Condon（FC）禁带，甚至比 REMPI 光谱中的 FC 允许带还要强。使用 Gaussian 进行理论计算在识别激发电子态的电子构型和预测跃迁能方面存在问题。然而，通过为第二激发电子态设置关键字，密度泛函理论和组态相互作用方法都可以定性地重现观察到的光谱。总的一致性极大地有助于振动分配。ZEKE 光谱表明，在保留中间电子态的振动激发方面存在倾向。此外，几乎所有的 ZEKE 光谱都表现出相似的振动分布，并且可以通过使用 Gaussian 09 从第一激发电子态的振子起源到阳离子态的 FC 计算来重现分布。这些结果表明，BghiP 在容纳额外电荷方面具有显著的结构稳定性。阳离子的所有观察到的振动带都是红外活性的，这确立了 ZEKE 光谱在为天体物理应用绘制远红外带方面的作用。
