Density and refractive index of solid layers of noble gases and sulphur hexafluoride

Abstract

The density and refractive index of solid layers of the noble gases (Ne, Ar, Kr, Xe) and SF₆ were measured as a function of the condensation conditions such as temperature, growth rate and layer thickness by an interferometric method during growth of the layer on a metal mirror substrate.

It is shown, that the density (ρ) and refractive index (n) are strongly dependent on the condensation temperature. For condensation temperatures T_K above a certain value T_ch, which is characteristic for each gas, ρ and n of the solid layers agree very well with those given in the literature for the bulk crystals. Below T_ch however, we find an approximately linear decrease of ρ and n with T_K. The changes in ρ and n with T_K, which can be as large as 30 % and 14 %, respectively, increase in a characteristic manner within the series Ne, Ar, Kr, Xe, SF₆, i.e., with increasing molecular weight. The experiments yield information on the structure of the layers and their aging behaviour. This knowledge is a necessary condition for the quantitative study of matrix isolated atoms or molecules, since their properties depend on their interaction with the matrix.