A semi-automatic examination of CO2 structures in thin films at low temperatures

Abstract

The aim of this paper is to study the IR spectra of thin films of a mixture of carbon dioxide and water obtained via vapor deposition in the temperature range of 11-180 K. Based on the analysis of the spectra, we examine the formation of hydrates and clathrates that are of interest to modern condensed matter physics. To carry out this research, the methods of IR spectroscopy, mass spectroscopy, and optical analysis of the thin films formed were utilized. Fourier transform infrared spectroscopy is one of the most reliable methods for the identification of the molecular composition and structural states of molecular mixtures. Additional tools, such as mass spectroscopy and interference patterns, were used to confirm the formation of specific structures in the carbon dioxide and water mixture. During the experiments, CO₂ hydrate and gas hydrate structures formed in the mixture. The gas hydrates that formed in the mixture can be classified as sI-type hydrates. The hydrate compounds hold CO₂ molecules in their structures, preventing them from sublimating at 93 K (the sublimation temperature of unbound CO₂ at a pressure of P = 0.5µTorr). At the same time, the sublimation temperature of CO₂ molecules bound in hydrate structures becomes equal to 147-150 K. For the selected concentration of CO₂ (25%) – H₂O (75%), the changes in the observed spectra and the data obtained using mass spectroscopy indicate incomplete hydration of the mixture. Some of the CO₂ molecules remain unbound and sublimate earlier. The increase in the refractive index as the concentration of H₂O in the mixture approaches 25% indicates the growth of structures that are less dense compared to amorphous CO₂ condensates and amorphous H₂O ice. The results expand the current knowledge of the clathrate and hydrate formation processes in mixtures of CO₂ and H₂O, their physical characteristics, and the emergence of certain characteristics depending on the method of formation.