Experimental evidence for wannier impurity states in doped rare-gas fluids

In this paper we present the results of an experimental study of the vacuum ultraviolet absorption spectra of Xe impurity in Ar (density range 0-1.4 g cm^ṫ) in Ne (density range 0.1-0.65 g cm^ṫ;) and in He (density range 0.04-0.1 g cm^ṫ;), spanning the energy region 8-11 eV. These experimental results provide new information regarding medium perturbations of the lowest extravalence impurity excitations and pertain to the observation of Wannier impurity states in a dense medium. We were able to identify low extravalence excitations of d symmetry which persist over the entire density range of the fluid. All the lowest extravalence excitations to states of s and d symmetry exhibit appreciable spectral blue-shifts at moderate and at high density of the fluid. New experimental evidence has been obtained for the identification of the n = 2 Wannier impurity state of Xe in liquid Ar, resulting in an estimate of the impurity ionization potential in the dense fluid. A qualitative relation has been established between the spectral shifts of the high Rydberg states in the atomic limit and the location of the n = 2 Wannier state as well as the impurity band gap in the liquid.