Structure of the Xe 6s and 6s' Rydberg states in supercritical Ar

In this paper, we present new absorption measurements and complete lineshape simulations (including all blue satellite bands) of the Xe 6s and 6s' Rydberg states doped into Ar from low density to the density of the triple point liquid, at both noncritical temperatures and on an isotherm near (+0.5$^{\circ}$C) the critical temperature of Ar. Using these simulations, as well as the known Ar induced shift of the ionization energy of a dopant\footnote{C. M. Evans and G. L. Findley, Phys. Rev. A 72, 022717 (2005).}, the Ar induced shift in the Xe 6s and 6s' term energies is determined and is shown to exhibit a large critical point effect. The nature of this critical point effect is discussed. \\ \emph{The experimental measurements reported here were performed at the University of Wisconsin Synchrotron Radiation Center (NSF DMR-0537588). This work was supported by grants from the Petroleum Research Fund, from the Professional Staff Congress--City University of New York, and from the Louisiana Board of Regents Support Fund.}