CO₂ Versus CH₄ Aggregation on Trifluorobenzene: Molecular Level Characterization via Rotational Spectroscopy

The cluster growth behavior of CO₂ and CH₄ on an aromatic ligand has been studied through the unambiguous identification of complex structures of 1,2,3-trifluorobenzene-(CO₂)_1-4 and -ß(CH₄)_1-2 using broadband rotational spectroscopy in conjunction with extensive theoretical calculations. The results reveal a contrast in the thermodynamically favorable ligand-gas binding sites and noncovalent interactions of the two gaseous molecules on the ligand. The observation of a tunneling splitting and large centrifugal distortions indicates that CH₄ molecules bind to the fluorinated π system via three weak hydrogen bonds without CH₄ self-interactions, resulting in an effective structure displaced toward the dissociation limit. Conversely, CO₂ shows diverse and stronger intermolecular interactions with the fluorinated benzene, including F─C tetrel bonding, lone pair to π-hole interactions, π-π stacking, and a significant contribution from CO₂ self-interactions. The thorough examination of ligand-gas interactions and aggregation patterns highlights the significant capacity and selectivity of the fluorinated aromatic ligand for accepting CO₂ over CH₄.