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The study of the electronic and thermophysical properties of fluid alkali metals near the gas-liquid critical point has attracted interest for decades for many technical and scientific reasons. It is the subject of numerous theoretical and experimental papers and various review articles (see e.g. Mott, 1974; Cusack, 1978; Hensel, 1980, 1982, 1984; Freyland, 1981; Yonezawa and Ogawa, 1982; Alekseev and Iakubov, 1983; Freyland and Hensel, 1985). However, considerable controversy still surrounds the exact nature of the gas-liquid critical point phase transition, in particular with regard to the role of the metal-nonmetal transition which occurs at reduced densities of the monovalent metals. The critical data are not known with sufficient certainty. A reliable theoretical prediction of such data is not possible.

A newly developed photoion-photoelectron Vacuum-UV coincidence spectrometer has been coupled to a supersonic metal atom cluster beam source and has been used to investigate the electronic structure of isolated mercury clusters in the size range from 1 to 110 at several selected discrete excitation energies between 11.3 and 7.1 eV. Excitation of the van der Waals cluster Hg10 at the center of the strong D3/2-autoionization line at 10.7 eV yields a photoelectron kinetic energy distribution between 0 and 2.5 eV indicating the population of Hg10 ionic states, which are also accessible by threshold ionization.

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ESCA measurements on a series of gold compounds reveal a monotonic relationship between binding energies of the Au 4f levels and formal oxidation states, and provides first evidence for the oxidation state –1 of gold in CsAu and RbAu.

The electronic absorption spectrum of the van der Waals dimer Hg2 has been measured in the UV–spectral range by a new supersonic jet direct absorption technique. The data led to an improved analysis of the X 10+g–G 10+u transition, yielding the parameters ω’e =79 cm−1, ωex’e =0.22 cm−1, and Re =3.00 A for the Morse potential of the G 10+u state.

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