Laboratory Studies of the Clathrate Hydrate Formation in the Carbon Dioxide-Water Mixtures at Interstellar Conditions

This study investigates the formation of carbon dioxide clathrate hydrates under conditions simulating interstellar environments, a process of significant astrophysical and industrial relevance. Clathrate hydrates, where gas molecules are trapped within water ice cages, play an essential role in both carbon sequestration strategies and understanding of the behavior of ices in space. We employed a combination of Fourier Transform Infrared (FTIR) spectroscopy, mass spectrometry, temperature-programmed desorption (TPD), and Density Functional Theory (DFT) calculations to explore thin films of H₂O:CO₂ ice mixtures with varying CO₂ concentrations (5-75%) prepared by vapor deposition at temperatures ranging between 11 and 180 K. The study revealed the influence of CO₂ concentration and deposition temperature on the formation mechanism of diverse structures, including clathrate hydrates, polyaggregates, and segregated CO₂ groups. Spectral features associated with CO₂ encapsulation in clathrate hydrates were observed at 2335, 2349, and 3698 cm^-1 in the 5 and 15% mixtures after deposition at 11 K and after warming at temperatures above 100 K. The observed increase in CO₂ sublimation temperature to 145-155 K and co-condensation of CO₂ molecules at 172 K with water molecules at a pressure of 0.5 μTorr can be attributed to the encapsulation of CO₂ molecules within the robust hydrogen-bonded framework of the clathrate cages under specific conditions. These findings enhance our understanding of the intricate processes involved in clathrate and hydrate formation in CO₂ and H₂O mixtures, shedding light on their physical properties and the dependence of their specific characteristics on the formation method.