ZERO-KINETIC-ENERGY PHOTOELECTRON-SPECTROSCOPY OF AR(2P)-EXCITED ARGON CLUSTERS

Zero-kinetic-energy photoelectron (ZEKE) spectra of atomic argon and a rgon clusters are recorded in the Ar(2p) excitation regime. Characteri stic shifts of the Ar(2p) ionization energies are observed as a functi on of cluster size. The maximum of the zero-kinetic-energy photoelectr on band (Ar(2P3/2)) is found at 248.9+/-0.1 eV, whereas the correspond ing band in the ZEKE spectrum of a cluster beam of average cluster siz e of approximately 750 atoms occurs at 247.94+/-0.01 eV. An enhanced Z EKE yield in the Ar(2p) continuum is attributed to inelastic scatterin g of the photoelectron within individual clusters. These results are c ompared to Ar(2p) spectroscopic studies of argon atoms, argon clusters and solid argon. Based on our analysis of the Ar(2p) ZEKE spectrum of large clusters, the Ar(2P3/2) ionization energy of solid argon is pre dicted to be 247.7+/-0.1 eV.