The rotational spectrum of the weakly bound molecular complex OC ··· HCN investigated by pulsed-nozzle, Fourier-transform microwave spectroscopy

Abstract

Abstract The technique of pulsed-nozzle, Fourier-transform microwave spectroscopy has been used to detect and assign the ground-state rotational spectrum of each of eleven isotopic species of a weakly bound molecular complex formed by carbon monoxide and hydrogen cyanide. The nature of the spectra is consistent with a linear complex. Accurate values of the rotational constants B0, the centrifugal distortion constants DJ and, where appropriate, the nuclear quadrupole coupling constant χaa(14N) or χaa(D) have been determined. For the most abundant species 16O12C ··· H12C14N, the results are: B0 = 1476.2925(1) MHz, DJ = 3.306(2) kHz and χaa(14N) = −4.285(1) MHz. When the B0 values are interpreted in terms of a simple model in which the nuclei are collinear in the order OC ··· HCN at equilibrium but with each rigid subunit executing a large amplitude oscillatory motion with respect to its centre of mass in the zero-point state, the mean values r(C ··· C) = 3.6698(2) and 3.66510(3)Aresult for the H- and D-bonded species, respectively. The intermolecular stretching force constant ka and the amplitude φav for the oscillation of the HCN subunit have been estimated from the spectroscopic constants DJ and χaa(14N), respectively.