Tuning Intermolecular Interactions for Chiral Analysis:\nThe Microwave Spectra and Molecular Structures of the Chiral Tag Candidates <i>cis</i>- and <i>trans</i>-2-Fluoro-3-(trifluoromethyl)oxirane\nand Their Gas-Phase Heterod

The <i>cis</i> and <i>trans</i> isomers of\nthe chiral tagging candidate molecule, 2-fluoro-3-(trifluoromethyl)oxirane,\nas well as the lowest energy gas-phase heterodimer of each with the\nargon atom, are characterized via quantum chemistry calculations and\nmicrowave rotational spectroscopy from 5 to 18 GHz and their ground\nstate, vibrationally averaged structures, are determined. Apart from\nthe <i>cis</i>/<i>trans</i> nature of the ring\nsubstitution and small differences in the dihedral angle specifying\nthe rotation of the trifluoromethyl group, the two oxirane molecules\nand their respective argon complexes each have remarkable structural\nsimilarity. In contrast, the binding mode of argon to the oxirane,\nwhile similar for the two complexes here, is distinct from those modes\nobserved in previous argon-fluorooxirane species. The ability to tune\nthe preferred mode of binding with differing levels of fluorine substitution\nmay prove advantageous in applications of chiral tagging to a wide\nvariety of analytes.