Innovative Laser Techniques for the Higher Resolution Electronic Spectroscopy of Molecular Ions

实验物理化学项目正在为纽约州立大学石溪分校的菲利普·M·约翰逊开发一种名为光诱导里德堡电离光谱(PIRI)的新激光光谱方法提供支持，该方法有望大幅提高分子阳离子光谱的分辨率。这项技术依赖于这样一个事实，即一个电子被激发到高里德堡态的中性分子的光学性质几乎与相应离子的光学性质相同。该方法通过制备处于略低于第一电离极限的高n里德堡态的中性分子来进行。然后，这些里德堡分子的离子核心被可调谐激光以电子方式激发，当离子发生转变时，导致自动电离。离子相对于波长的产生产生的光谱等同于光电子光谱，但不受电子能量分析仪分辨率的限制。PIRI能够检测离子的激发电子态，这是以前的高分辨率阈值电离技术如零动能电子能谱和质量分析阈值电离光谱无法获得的。这项新技术将应用于几个与大气有关的小分子，以便在收集有关这些重要物种的新信息的同时探索该方法的参数和能力。光诱导里德堡电离光谱或PIRI将使人们能够以以前无法达到的分辨率观察分子阳离子的电子光谱。这将首次获得有关离子密集激发电子态的转动和振动信息。最初的实验将集中在氧、水、二氧化碳、氯化氢和二氧化硫的离子状态上。

The Experimental Physical Chemistry Program is providing support for Philip M. Johnson of the State University of New York-Stony Brook to develop a new method of laser spectroscopy, called photoinduced Rydberg ionization spectroscopy (PIRI), which promises a substantial improvement in the resolution attainable in the spectra of molecular cations. This technique relies upon the fact that the optical properties of neutral molecules with one electron excited to a high Rydberg state are almost identical to those of the corresponding ion. The method proceeds by preparing a neutral molecule in a high-n Rydberg state just below the first ionization limit. The ion cores of these Rydberg molecules are then electronically excited by a tunable laser, resulting in autoionization when an ion transition occurs. The production of ions with respect to wavelength produces spectra which are equivalent to photoelectron spectra but are not restricted by the resolution of electron energy analyzers. PIRI is able to examine the excited electronic states of ions which are not accessible to previous high resolution threshold ionization techniques such as zero kinetic energy electron spectroscopy and mass analyzed threshold ionization spectroscopy. This new technique will be applied to several small molecules of atmospheric interest in order to explore the parameters and capabilities of the method while gathering new information about these important species. Photoinduced Rydberg ionization spectroscopy or PIRI will enable the electronic spectroscopy of molecular cations to be observed with a resolution previously unattainable. For the first time, rotational and vibrational information on congested excited electronic states of ions will be acquired. Initial experiments will focus on ionic states of oxygen, water, carbon dioxide, hydrogen chloride and sulfur dioxide.