Evolution of excitonic bands in fluid xenon

Reflection spectra of homogeneous fluid xenon are presented for the wavelength region 115<λ<165 nm and densities ranging from that near the critical point to that at the triple point. For each atomic line in this spectral region two bands are observed: one broadened and somewhat shifted band corresponding to the atomic transition, and another distinct band corresponding in position to that of the exciton observed in the triple-point liquid. Dispersion analysis of the two (atomic and excitonic) ³P₁ bands yielded the optical constants ε^', ε^'', n, and k as a function of photon energy as well as parameters of the absorption bands. The results are interpreted in terms of exciton transitions appearing in momentary clusters of the fluid. The analysis of the parameters of the absorption bands was compared with the statistical fluctuations of the fluid density. It was estimated from this comparison that the ³P₁ exciton can be formed in a momentary cluster of atoms provided two conditions are fulfilled: the cluster has at least the volume of 1.5×{}10^-21 cm³ and contains at least ten atoms.