H₃P⋯AgI: Generation by laser-ablation and characterization by rotational spectroscopy and: Ab initio calculations

The new compound H₃P⋯AgI has been synthesized in the gas phase by means of the reaction of laser-ablated silver metal with a pulse of gas consisting of a dilute mixture of ICF₃ and PH₃ in argon. Ground-state rotational spectra were detected and assigned for the two isotopologues H₃P⋯¹⁰⁷AgI and H₃P⋯¹⁰⁹AgI in their natural abundance by means of a chirped-pulse, Fourier-transform, microwave spectrometer. Both isotopologues exhibit rotational spectra of the symmetric-top type, analysis of which led to accurate values of the rotational constant B₀, the quartic centrifugal distortion constants D_J and D_JK, and the iodine nuclear quadrupole coupling constant χ_aa(I) = eQq_aa. Ab initio calculations at the explicitly-correlated level of theory CCSD(T)(F12∗)/aug-cc-pVDZ confirmed that the atoms P⋯Ag-I lie on the C₃ axis in that order. The experimental rotational constants were interpreted to give the bond lengths r₀(P⋯Ag) = 2.3488(20) Å and r₀(Ag-I) = 2.5483(1) Å, in good agreement with the equilibrium lengths of 2.3387 Å and 2.5537 Å, respectively, obtained in the ab initio calculations. Measures of the strength of the interaction of PH₃ and AgI (the dissociation energy D_e for the process H₃P⋯AgI = H₃P + AgI and the intermolecular stretching force constant F_P⋯Ag) are presented and are interpreted to show that the order of binding strength is H₃P⋯HI < H₃P⋯ICl < H₃P⋯AgI for these metal-bonded molecules and their halogen-bonded and hydrogen-bonded analogues.