Density of CH4CH4, N2N2 and CO2CO2 ices at different temperatures of deposition

In this work the density (ρρ) and the real part of the refractive index (n)(n) of frozen methane, nitrogen and carbon dioxide were obtained in the laboratory. The densities are given for different temperatures of deposition between 10 K and the sublimation temperature of these molecules in our experimental setup (p⩽10-7mbar). We have found that methane and nitrogen have a constant value in all the interval of the studied temperatures for both ρρ and nn. Carbon dioxide, on the contrary, has important variations for both physical parameters (up to 50% in density) revealing important structural changes.