Molecular Geometries and Other Properties of H2O⋯AgI and H3N⋯AgI as Characterised by Rotational Spectroscopy and Ab Initio Calculations

The rotational spectra of H3N∙∙∙AgI and H2O∙∙∙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 H3N∙∙∙AgI and six isotopologues of H2O∙∙∙AgI. Rotational constants, B0; centrifugal distortion constants, DJ, DJK or J, JK; and the nuclear quadrupole coupling constants, χaa(I) and χbb(I)χcc(I) are reported. H3N∙∙∙AgI is shown to adopt a geometry that has C3v symmetry. The geometry of H2O∙∙∙AgI is Cs at equilibrium but with a low barrier to inversion such that the vibrational wavefunction for the v = 0 state has C2v 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, H3N, H2O, H2S, H3P or CO). The results of experiments are reported alongside those of ab initio calculations at the CCSD(T)(F12*)/AVXZ level (X=T,Q).