Infrared spectroscopy of clathrate hydrates for planetary science: the ethylene case.

Hydrocarbons are observed in the gas or solid phases of solar system objects, including comets, Trans-Neptunian Objects, planets and their moons. In the presence of water ice in these environments, hydrocarbons-bearing clathrate hydrates could form. In clathrate hydrates, guest molecules are trapped in crystalline water cages of different sizes, a phase used in models of planetary (sub-)surfaces or icy bodies such as comets. The phases in presence, the potential estimate of abundances of hydrocarbon species, the spectroscopic behaviour of hydrocarbon species in the different phases must be recorded to provide reference spectra for the comparison with remote observations. We show in this study the specific encaged ethylene signatures, with bands similar in position, but shifted from the pure ethylene ice spectrum. They show a marked temperature dependence both in position and width. Some vibrational modes are activated in the infrared by interaction with the water ice cages.