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

TL;DR

This study investigates the infrared spectral signatures of ethylene in hydrocarbon clathrate hydrates, revealing temperature-dependent shifts and interactions with water ice cages relevant for planetary science observations.

Contribution

It provides the first detailed infrared spectral data of ethylene in clathrate hydrates, highlighting temperature effects and vibrational mode activation for planetary surface models.

Findings

Ethylene shows shifted IR bands in clathrate form.

Spectral features depend on temperature.

Water cages activate certain vibrational modes.

Abstract

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.