Zhang Jie, Pei Linsen, Kong Wei
Department of Chemistry, Oregon State University, Corvallis, OR 97331-4003, USA.
J Chem Phys. 2008 Mar 14;128(10):104301. doi: 10.1063/1.2837467.
Far infrared (FIR) spectroscopy of polycyclic aromatic hydrocarbons is of particular interest to astrophysics since vibrational modes in this range are representative of the molecular size and shape. This information is hence important for identification of chemical compositions and for modeling of the IR spectrum observed in the outer space. In this work, we report neutral and cation FIR spectroscopy of tetracene vaporized from a laser desorption source. Results from two-color resonantly enhanced multiphoton ionization and two-color zero kinetic energy photoelectron spectroscopy will be presented. Several skeletal vibrational modes of the first electronically excited state of the neutral species and those of the cation are assigned, with the aid of ab initio and density functional calculations. The adiabatic ionization potential is determined to be 55 918 +/- 7 cm(-1). Interestingly, all observed vibrational modes can be rationalized based on a simple Huckle calculation, i.e., by observing the addition or elimination of nodal planes due to electronic excitation and/or ionization. Limited by the Franck-Condon principle and the rigidity of the molecular frame of tetracene, only IR forbidden modes are observed in this work.
多环芳烃的远红外（FIR）光谱对天体物理学尤为重要，因为该范围内的振动模式代表了分子的大小和形状。因此，这些信息对于识别化学成分以及对外层空间观测到的红外光谱进行建模非常重要。在这项工作中，我们报告了从激光解吸源蒸发的并四苯的中性和阳离子FIR光谱。将展示双色共振增强多光子电离和双色零动能光电子能谱的结果。借助从头算和密度泛函计算，对中性物种第一电子激发态和阳离子的几种骨架振动模式进行了归属。绝热电离势确定为55918±7cm⁻¹。有趣的是，所有观察到的振动模式都可以基于简单的休克尔计算进行合理解释，即通过观察由于电子激发和/或电离导致的节点平面的增加或消除。受弗兰克 - 康登原理和并四苯分子框架刚性的限制，在这项工作中仅观察到红外禁阻模式。
