Photoelectron and Photoionization Spectroscopy of Metal-Organic Complexes

美国肯塔基大学的杨东升教授在实验物理化学项目的支持下，研究了配位不饱和气态金属有机配合物的电子光谱、金属配体结合、电子态和分子结构。金属有机体系包括DNA和RNA核碱基的锂、铝、钪和铜配合物、多环芳烃和多苯基。这些配合物是在激光汽化分子束中制备的，用光电离质谱法进行鉴定，并用紫外（UV）和红外(IR)-紫外脉冲场电离-零电子动能（ZEKE）光电子和光电离光谱法进行研究。紫外ZEKE实验测量了精确的电离能和低频金属配体的拉伸和弯曲，而红外-紫外ZEKE和光电离实验确定了这些系统的高频配体振动模式。电离能是分子的关键热化学性质之一，是将金属原子的电离能与阳离子的键能结合得到金属-配体的中性键能。金属-配体的拉伸和弯曲为金属-配体结合提供了直接证据，而配体的高频振动则探测了金属配位引起的配体几何形状的变化。结合光谱数据和理论预测确定电子状态和分子结构。这个研究项目将带来关于金属原子与分子结合的复合物的结构和能量学的新知识。研究结果将对有机金属化学、生物化学、催化和材料合成领域的实践者产生兴趣。该项目为学生和博士后提供技术上具有挑战性的研究培训机会，为他们未来的就业做好有效的准备。

Dong-Sheng Yang of the University of Kentucky is supported by the Experimental Physical Chemistry Program to investigate the electronic spectra, metal-ligand binding, electronic states, and molecular structures of coordinatively unsaturated gaseous metal-organic complexes. The metal-organic systems include lithium, aluminum, scandium, and copper complexes of DNA and RNA nucleobases, polycyclic aromatic hydrocarbons, and polyphenyls. These complexes are prepared in laser-vaporization molecular beams, identified with photoionization mass spectrometry, and studied using ultraviolet (UV) and infrared (IR)-UV pulsed field ionization-zero electron kinetic energy (ZEKE) photoelectron and photoionization spectroscopy. The UV ZEKE experiments measure precise ionization energies and low frequency metal-ligand stretches and bends, whereas the IR-UV ZEKE and photoionization experiments determine the high-frequency ligand vibrational modes of these systems. The ionization energy is one of the key thermochemical properties of a molecule and is used to obtain the metal-ligand neutral bond energy by combining the ionization energy of the metal atom and the bond energy of the cation. The metal-ligand stretches and bends give direct evidence about the metal-ligand binding, whereas the high-frequency ligand vibrations probe changes in the ligand geometry induced by metal coordination. Combining the spectroscopic data and theoretical predictions determines electronic states and molecular structures. This research project will lead to new knowledge about the structure and energetics of complexes made up of metal atoms binding to molecules. The results will be of interest to practitioners in organometallic chemistry, biochemistry, catalysis, and materials synthesis. This project provides technologically challenging research training opportunities for students and postdoctoral associates to prepare them effectively for future employment.