Gaseous Clusters of Fluorocarbons and Carbon Dioxide: Modeling Solvation by Supercritical Carbon Dioxide

In this study, chirped-pulse Fourier-transform microwave spectroscopy (CP-FTMW) has been used to analyze carbon dioxide (CO₂)-containing molecular clusters cooled by adiabatic expansion. CO₂ has been gaining attention as a supercritical (sc) solvent for use in industrial applications due its abundance, non-toxicity and ability to change its solvation properties with temperature and pressure. sc-CO₂ is currently used for applications like decaffeinating coffee, but its ability to dissolve smaller molecules is not well quantified. Adiabatically cooled gas clusters have been shown to mimic the dynamics of solvation shells, which provides a safer and cheaper way to model solvation. In this project, small, fluorinated organic compounds were analyzed, since high bond polarities in the carbon-fluorine bonds typically result in good solubilities in sc-CO₂. Trifluoroethylene (C₂HF₃), propene (C₃H₆), and 3-fluoropropene (C₃H₅F) were selected due to their wide range of polarities and fluorination. Experimental results include CP-FTMW spectra of trifluoroethylene with up to six CO₂ molecules, with CO₂ primarily interacting with the fluorine atoms and the electron-deficient hydrogen atom. In contrast, propene is predicted to form clusters where CO₂ primarily interacts with the π-bond.