CORE-LEVEL BINDING-ENERGY SHIFTS AND POLARIZATION SCREENING - A COMBINED EXPERIMENTAL AND THEORETICAL-STUDY OF ARGON CLUSTERS

Photoelectron spectra of the argon 2p core level for free argon cluste rs of up to 4000 atoms are compared to detailed calculations. The comp arison shows that the size-dependent shifts of the core level binding energy can be explained in a pure polarization-screening model. Import ant differences arise between the shifts for the bulk (interior) and t he surface atoms. The agreement between experiment and theory allows t he extrapolation of the cluster data to the ''infinite'' solid. In thi s way we obtain the shifts of the core level binding energy between th e free atom, the surface atom and the bulk of argon. The relation betw een these shifts and those of the first ionization potential is discus sed. (C) 1996 American Institute of Physics.