The σ-Hole Interaction Between Sulfur Hexafluoride and Ammonia Characterised by Broadband Rotational Spectroscopy

A weakly-bound complex of SF6 and NH3 is generated within an expanding gas jet and characterised by broadband rotational spectroscopy. The spectra of isotopologues (SF6NH3)-S-32-N-14, (SF6ND3)-S-32-N-14, (SF6NH3)-S-32-N-15 and (SF6NH3)-S-34-N-15 are observed and assigned to determine the spectroscopic parameters. These parameters are consistent with the complex having a C-3v symmetric rotor geometry, in which the nitrogen atom of NH3 coordinates to SF6 such that the C-3v axis of the NH3 sub-unit is aligned with a local C-3 axis on the SF6 sub-unit. The geometry of the complex is rationalized in terms of a sigma-hole interaction. The observed spectra and ab initio calculations also reveal evidence of internal dynamics involving internal rotation of one monomer sub-unit with respect to the other about the symmetry axis of the complex.