The rotational spectrum and molecular geometry of an antihydrogen-bonded dimer of sulfur dioxide and hydrogen cyanide

The ground-state rotational spectra of the four isotopic species (32SO2,HC14N), (32SO2,DC14N), (32SO2,HC15N), and (34SO2,HC14N) of a weakly bound dimer of sulfur dioxide and hydrogen cyanide have been observed by means of pulsed-nozzle, Fourier-transform microwave spectroscopy. The 14N-nuclear quadrupole coupling constants determined for the isotopomer (32SO2,HC14N) of this asymmetric rotor molecule are χaa =−2.876(3) MHz and χbb =2.025(4) MHz while the rotational and centrifugal distortion constants are (A0−ΔK) =8633.849(1) MHz, B0=1848.890(2) MHz, C0=1615.863(2) MHz, ΔJ =9.56(1) kHz, ΔJK =114.84(7) kHz, δJ =0.838(6) kHz, and δK =89(1) kHz. The spectroscopic constants have been interpreted in terms of a nonplanar, antihydrogen-bonded geometry of Cs symmetry with S, H, C, and N nuclei lying in the symmetry plane. The HCN molecule is roughly perpendicular to the plane of the SO2 molecule with N lying between the SO2 plane and the H atom. The distance between the SO2 and HCN centers of mass is rc.m. =3.6542(1) Å. The angle between the C2 axis of the SO2 subunit and the NCH axis is 86° and the two axes intersect at a distance of 1.38 Å above the S nucleus.