The geometry and intermolecular binding of HCN…BrC1 probed by rotational spectroscopy

Ground-state rotational spectra of several isotopomers of a linear complex formed between HCN and BrCl were observed by pulsed-nozzle, F-T microwave spectroscopy and analysed to give the spectroscopic constants B0, DJ, χ(Br), χ(Cl), and Mbb(Br). The order HCN…BrCl of the nuclei was established from the changes in the B0 values on isotopic substitution. The small fractional electronic charge (δ ≈ 0.05) transferred from Br to Cl on complex formation and the intermolecular stretching force constant (kσ ≈ 11 N m−1) estimated from the spectroscopic constants indicates a weak interaction of HCN and BrCl, with little perturbation of the charge distribution of BrCl.