Microwave Spectra and Molecular Structures of the Gas-Phase Heterodimers Formed between Argon and 3,3,3-Trifluoropropene and between Acetylene and 3,3,3-Trifluoropropene

The gas-phase heterodimers formed by argon and acetylene with 3,3,3-trifluoropropene are investigated using <i>ab initio</i> calculations and Fourier transform microwave spectroscopy. Spectroscopic constants of the most abundant isotopologues of these two complexes, as well as their minor isotopologues containing a single ¹³C substitution, reveal their structures. Ar is located above the planar HCCCF cavity of the trifluoropropene so that it can interact with a maximum number of heavy atoms. Acetylene binds to the H atom of trifluoropropene geminal with the CF₃ group, and lies in the symmetry plane of trifluoropropene. One of the acetylenic H atoms forms a bifurcated hydrogen bond with both out-of-plane fluorine atoms, and the acetylenic bond interacts with the geminal H atom. The proximity of this H atom to the CF₃ group suggests that this motif is driven by electrostatic factors.