Study of Zero Kinetic Energy Photoelectron Spectroscopy of Organic van der Waals Molecules. Determination of Adiabatic Ionization Potentials

本课题组于1993年在日本立野口科学技术研究所建立了一套新的双色零动能（ZEKE）光电子能谱仪。在AEKE光电子测量中引入双脉冲场技术，进一步提高了能量分辨率，并成功地应用于MATI中在双色ZEKE测量中，使用两个ns激光器，一个用于激发到特定的激发态，另一种是进一步激发到非常高的里德堡态，仅比电离阈值低几个波数。为了进行非常高分辨率的ZEKE电子的测量，（小于一个波数），我们施加了两种具有适当延迟时间的脉冲电场，一种是除去所有发射的光电子以及一些很浅的里德伯电子，另一种是收集较深的Rydberg电子，本文所研究的分子是一些苯衍生物和高级芳香分子（苯甲腈、氟苯、茴香硫醚、四氟苯、萘、吲哚等）并且它们的货车德瓦耳斯络合物主要与超音速射流中的氩络合。结果表明，我们成功地测定了这些分子种类的绝热电离势，包括在喷流中形成的货车范德华复合物。我们还能够从ZEKE光电子能谱中观察到货车范德华正离子的货车范德华振动频率。

A new apparatus of two-color zero-kinetic-energy (ZEKE) photoelectron spectrometer with a compact, high-resolution, high-brightness ZEKE electronanalyzer earlier developedin our group, has been set up at the Japan Advanced Institute of Science and Technology here at Tatsunokuchi since 1993. The energy resolution has been further improved by introducing a "two-pulsed-field" technique in our AEKE photo-electron measurements, and this technique has been successfully applied to our MATI (Mass Analyzed Threshold Ionization Spectroscopy).In the two-color ZEKE measurements, two ns lasers are used, one is for excitation to a specific excited state, and the other is for further excitation to very high Rydberg states just a few wavenumber below the ionization threshold. In order to carry out measurements of very high resolution ZEKE electrons (less than one wavenumber), we have applied two kinds of pulsed electricfields with an appropriatedelay time, one is to remove all the emitted photoelectrons as well as some very shallow Rydberg electrons, and the other is to collect somewhat deeper Rydberg electrons.The molecules studied in the present work are some benzene derivatives and higher aromatic molecules (benzonitrile, fluorobenzene, thioanisole, tetrafluorobenzene, naphthalene, indole, etc.) and their van der Waals complexes mainly with argon in supersonic jets. As results, we have successfully determined the adiabatic ionization potentials of these molecular species including van der Waals complexes formedin jets. We have also been able to observe van der Waals vibrational frequencies of the van der Waals cations from ZEKE photoelectron spectra.