Novel measurements of refractive index, density and mid-infrared integrated band strengths for solid O2, N2O and NO2:N2O4 mixtures

We present novel measurements of the refractive index, density and integrated band strengths of mid-infrared features of solid N₂O at 16 K and of NO₂ and N₂O₄ in two frozen NO₂:N₂O₄ mixtures deposited at 16 and 60 K. The refractive index and density measurements were performed also for frozen O₂ deposited at 16 K. In this case, the integrated band strength values could not be determined since O₂ is a homonuclear molecule and therefore its fundamental mode is not infrared active. The solid samples were analysed by infrared spectroscopy in the 8000÷800 cm⁻¹ range. The sample thickness was measured by the interference curve obtained using a He–Ne laser operating at 543 nm. The refractive index at this laser wavelength was obtained, by numerical methods, from the measured amplitude of the interference curve. The density values were obtained using the Lorentz–Lorenz relation. Integrated band strength values were then obtained by a linear fit of the integrated band intensities plotted versus column density values. The astrophysical relevance of these novel measurements is briefly discussed.