Wörner H J, Merkt F
Laboratorium für Physikalische Chemie, ETH-Zürich, 8093 Zürich, Switzerland.
J Chem Phys. 2007 Jul 21;127(3):034303. doi: 10.1063/1.2748049.
The electronic and rovibronic structures of the cyclopentadienyl cation (C(5)H(5) (+)) and its fully deuterated isotopomer (C(5)D(5) (+)) have been investigated by pulsed-field-ionization zero-kinetic-energy (PFI-ZEKE) photoelectron spectroscopy and ab initio calculations. The vibronic structure in the two lowest electronic states of the cation has been determined using single-photon ionization from the X (2)E(1) (") ground neutral state and 1+1(') resonant two-photon ionization via several vibrational levels of the A (2)A(2) (") excited state. The cyclopentadienyl cation possesses a triplet ground electronic state (X(+) (3)A(2) (')) of D(5h) equilibrium geometry and a first excited singlet state (a(+) (1)E(2) (')) distorted by a pseudo-Jahn-Teller effect. A complete analysis of the Emultiply sign in circlee Jahn-Teller effect and of the (A+E)multiply sign in circlee pseudo-Jahn-Teller effect in the a(+) (1)E(2) (') state has been performed. This state is subject to a very weak linear Jahn-Teller effect and to an unusually strong pseudo-Jahn-Teller effect. Vibronic calculations have enabled us to partially assign the vibronic structure and determine the adiabatic singlet-triplet interval (1534+/-6 cm(-1)). The experimental spectra, a group-theoretical analysis of the vibronic coupling mechanisms, and ab initio calculations were used to establish the topology of the singlet potential energy surfaces and to characterize the pseudorotational motion of the cation on the lowest singlet potential energy surface. The analysis of the rovibronic photoionization dynamics in rotationally resolved spectra and the study of the variation of the intensity distribution with the intermediate vibrational level show that a Herzberg-Teller mechanism is responsible for the observation of the forbidden a(+) (1)E(2) (')<--A (2)A(2) (") photoionizing transition.
通过脉冲场电离零动能（PFI-ZEKE）光电子能谱和从头算，研究了环戊二烯基阳离子（C(5)H(5) (+)）及其完全氘代同位素体（C(5)D(5) (+)）的电子结构和振转电子结构。利用从X (2)E(1) (")基态中性态的单光子电离以及通过A (2)A(2) (")激发态的几个振动能级的1+1(')共振双光子电离，确定了阳离子两个最低电子态的振转结构。环戊二烯基阳离子具有D(5h)平衡几何结构的三重基态电子态（X(+) (3)A(2) ('))和因赝 Jahn-Teller 效应而畸变的第一激发单重态（a(+) (1)E(2) ('))。对a(+) (1)E(2) (')态中的完全Emultiply sign in circlee Jahn-Teller效应和(A+E)multiply sign in circlee赝 Jahn-Teller效应进行了完整分析。该态受到非常弱的线性 Jahn-Teller 效应和异常强的赝 Jahn-Teller 效应的影响。振转计算使我们能够部分归属振转结构并确定绝热单重-三重间隔（1534±6 cm(-1)）。实验光谱、振转耦合机制的群论分析以及从头算被用于建立单重态势能面的拓扑结构，并表征阳离子在最低单重态势能面上的赝旋转运动。对转动分辨光谱中的振转光电离动力学分析以及对强度分布随中间振动能级变化的研究表明，Herzberg-Teller 机制是观察到禁戒的a(+) (1)E(2) (')<--A (2)A(2) (")光电离跃迁的原因。
