Evolution of intermediate excitons in fluid argon and krypton

Reflectivity spectra of fluid argon and krypton are reported for number densities ranging from ρ∼${10}^{21}$ ${\mathrm{cm}}^{\mathrm{-}3}$ to that of the triple-point liquid, complemented by spectra of solid samples near the triple point. Dispersion analysis by a decomposition into Lorentzians of the complex dielectric constant spectra (yielding reflectivities that fit the experimental values) revealed the existence of ‘‘extra’’ absorption bands in the immediate vicinity of the ${}_{}{}^3{}_{}{}^{}\mathrm{P}_1^{}{}_{}{}^{}$ and ${}_{}{}^1{}_{}{}^{}\mathrm{P}_1^{}{}_{}{}^{}$ atomic resonance lines, growing very rapidly with density; these bands were identified as corresponding to the n=1 Γ((3/2)) and n’=1 Γ((1/2)) intermediate excitons in the solid. Comparing the evolution of the n=1 exciton in fluid krypton with density fluctuations leads to the conclusion that for the creation of this exciton a momen- tary minimum local density of ${10}^{22}$ ${\mathrm{cm}}^{\mathrm{-}3}$ is needed within a certain small volume (1.2×${10}^{\mathrm{-}21}$ ${\mathrm{cm}}^3$). The results are also discussed in terms of a recent theory on localization in topologically disordered systems. Results on the changes in characteristic parameters, like line separations, widths, and oscillator strengths are presented.