Evolution of intermediate excitons in fluid argon and krypton

Abstract

Reflectivity spectra of fluid argon and krypton are reported for number densities ranging from \ensuremath{\rho}\ensuremath{\sim}${10}^{21}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$ 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 \ensuremath{\Gamma}((3/2)) and n'=1 \ensuremath{\Gamma}((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 ${10}^{22}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$ is needed within a certain small volume (1.2\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}21}$ ${\mathrm{cm}}^{3}$). 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.