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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 ΔJ , ΔJK ; 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, χaa(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). [ABSTRACT FROM AUTHOR]

• Chalcogen bonds. • Trimethylamine...Carbonyl sulphide. • Rotational spectra. • Isotopologues. • Geometry. • Internal dynamics. Rotational spectra of 5 isotopologues of (CH 3) 3 N⋯S C O were observed by chirped-pulse, Fourier-transform microwave spectroscopy. Spectroscopic constants B 0 , D J , D JK and the 14N nuclear quadrupole coupling constant χ aa (14N) determined for the symmetric-top isotopologues (CH 3) 3 N⋯S C O, (CH 3) 3 N⋯34S C O, (CH 3) 3 N⋯S 13C O, (CD 3) 3 N⋯S C O and (12CH 3) 2 (13CH 3)14N⋯S C O show that the intermolecular binding involves a chalcogen bond to S rather than O. Changes in various properties (the distance r (N⋯S) and the force constants k σ and k θθ associated with intermolecular stretching and angular oscillation θ of the trimethylamine subunit, respectively) from those of H 3 N⋯S C O allow for the effect of complete methylation of NH 3 on the chalcogen bond to be assessed. [ABSTRACT FROM AUTHOR]