van-der-waals Vibrations of Aromatic-Argon Cations Studied by ZEKE-Electron Spectroscopy K.Kimura Abstract: This article is to review van der Waals(vdW) vibrations' which have been observed for many kinds of aromatic-argon vdW complexes produced in supersonic jets.The main characteristics of zero-kinetic-energy(ZEKE)electron spectroscopy for studying vdW complexes are also described briefly.For the aromatic-argon vdW complexes so far studied, it is pointed out that the stretching mode is in a range of 40-60 cm-1,and the bending mode is in a range of 10-40cm-1.