Cation spectroscopy of aromatic-argon van der Waals complexes by ZEKE photoelectron spectra

This article is concerned with the application of two-color ZEKE (zero kinetic energy) photoelectron spectroscopy to weakly bounded aromatic-argon van der Waals (vdW) complexes in supersonic jets. A two-color ZEKE photoelectron technique gives us a very high resolution 'cation spectroscopy'. In this article, we describe what kinds of spectroscopic information can be deduced about the cations of vdW complexes from ZEKE photoelectron spectra, by mentioning mainly four examples, namely, (1) aniline-Ar and -Ar-2, (2) benzonitrile-Ar and -Ar-2, (3) pyrimidine-Ar and -Ar-2, and (4) azulene-Ar. We focus our attention mainly on (1) the energy shifts in the first adiabatic ionization energies of the aromatic molecules by complex formation and (2) the low-frequency vdW vibrations. Characteristics of two-color ZEKE photoelectron spectroscopy are also mentioned. The first adiabatic ionization energies (I-a) of these vdW complexes are summarized (Table 1), together with many other aromatic-argon vdW complexes, that were studied by the author's group. (C) 2000 Elsevier Science B.V. All rights reserved.