Molecular geometries and other properties of H 2 O⋯AgI and H 3 N⋯AgI as characterised by rotational spectroscopy and ab initio calculations.

The rotational spectra of H ₃ N⋯AgI and H ₂ O⋯AgI have been recorded between 6.5 and 18.5 GHz by chirped-pulse Fourier-transform microwave spectroscopy. The complexes were generated through laser vaporisation of a solid target of silver or silver iodide in the presence of an argon gas pulse containing a low concentration of the Lewis base. The gaseous sample subsequently undergoes supersonic expansion which results in cooling of rotational and vibrational motions such that weakly bound complexes can form within the expanding gas jet. Spectroscopic parameters have been determined for eight isotopologues of H ₃ N⋯AgI and six isotopologues of H ₂ O⋯AgI. Rotational constants, B ₀ ; centrifugal distortion constants, D _J , D _JK or Δ _J , Δ _JK ; and the nuclear quadrupole coupling constants, χ _aa (I) and χ _bb (I) - χ _cc (I) are reported. H ₃ N⋯AgI is shown to adopt a geometry that has C _3v symmetry. The geometry of H ₂ O⋯AgI is C _s at equilibrium but with a low barrier to inversion such that the vibrational wavefunction for the v = 0 state has C _2v symmetry. Trends in the nuclear quadrupole coupling constant of the iodine nucleus, χ _aa (I), of L⋯AgI complexes are examined, where L is varied across the series (L = Ar, H ₃ N, H ₂ O, H ₂ S, H ₃ P, or CO). The results of experiments are reported alongside those of ab initio calculations at the CCSD(T)(F12*)/AVXZ level (X = T, Q).