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

自1993年以来，一台新的双色零动能(ZEKE)光电子能谱装置已经在这里的Tatsunokuchi的日本先进科学技术研究所建立起来，该装置使用了我们小组早期开发的紧凑、高分辨率、高亮度的ZEKE电子分析仪。通过在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，该技术已成功地应用于我们的质量分析阈值电离谱。在双色Zeke测量中，使用了两个ns激光，一个用于激发特定的激发态，另一个用于进一步激发到仅低于电离阈值几波数的很高的里德堡态。为了对极高分辨率的Zeke电子(小于一个波数)进行测量，我们施加了两种具有适当延迟时间的脉冲电场，一种是去除所有发射的光电子和一些很浅的里德堡电子，另一种是收集一些较深的里德堡电子。本文研究的分子是一些苯衍生物和更高的芳香族分子(苯腈、氟苯、硫代苯甲醚、四氟苯、萘、吲哚等)。以及他们的范德华络合物，主要是在超音速喷气中与Ar形成的络合物。作为结果，我们成功地测定了这些分子物种的绝热电离势，包括形成喷注的范德华络合物。我们还从Zeke光电子能谱中观察到了van der Waals阳离子的van der Waals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.