Densities and refractive indices of ethane and ethylene at astrophysically relevant temperatures

Abstract

[EN] We report the density and refractive index, at 633 nm, of ethane and ethylene ices at temperatures from 13 to 65 K, measured by double laser interferometry and a cryogenic quartz crystal microbalance in a high vacuum chamber. Both quantities rise with the temperature of deposition from 13 K up to a plateau, 40 K for ethane and 22 K for ethylene. An amorphous structure is suggested for temperatures below 40 K for ethane and below 20 K for ethylene. Above these temperatures, 40 K for ethane and 20 K for ethylene, a crystalline structure is proposed. Ethylene results deviate from linear growth between 25 and 35 K, where a metastable structure is reported in the literature. Density values increase from about 0.40 to 0.60 g cm(-3) for ethane and from about 0.45 to almost 0.65 g cm(-3) for ethylene. The real part of the refractive index changes from about 1.27 to 1.45 for ethane and from about 1.30 to almost 1.48 for ethylene. Results are relevant especially to the outer Solar System, where the presence of these molecules is reported, and for experiments involving them. (C) 2017 Elsevier Inc. All rights reserved.