K-SHELL SPECTROSCOPY OF AR CLUSTERS

Total ion yield spectra of a supersonic beam of Ar clusters have been recorded in the Ar K-shell (1s) spectral region using synchrotron radi ation. The spectrum of the cluster component of beams containing argon clusters of mean size NBAR almost-equal-to 400 atoms is similar to th at of the x-ray absorption spectrum of solid Ar. Analysis of the Ar ls extended x-ray absorption fine structure (EXAFS) indicates an average first shell Ar-Ar distance in the cluster similar to that of the soli d, but there is an increased Debye-Waller (disorder/thermal motion) te rm as well as changes in the higher coordination shell signals.Time-of -flight mass spectra and photoion-photoion coincidence (PIPICO) spectr a of argon cluster beams are reported and the charge separation mechan isms of multiply charged argon clusters are discussed. The results are compared to those from recent studies of the Ar 2p spectra of Ar clus ters.