Rotational spectrum of the gas-phase dimer OC⋯BrCl

Abstract

The ground-state rotational spectra of the six isotopomers ¹⁶O¹²C⋯⁷⁹Br³⁵Cl, ¹⁶O¹²C⋯⁸¹Br³⁵Cl, ¹⁶O¹²C⋯⁷⁹Br³⁷Cl, ¹⁶O¹²C⋯⁸¹Br³⁷Cl, ¹⁶O¹³C⋯⁷⁹Br³⁵Cl, and ¹⁶O¹³C⋯⁸¹Br³⁵Cl, of a dimer formed by carbon monoxide and bromine monochloride have been observed by pulsed-nozzle, Fourier-transform microwave spectroscopy. The rotational constant B₀, the centrifugal distortion constant D_J and the halogen nuclear quadrupole coupling constants χ_aa(X), where X = Cl or Br, have been interpreted to give the properties of the weakly bound complex. It was found that the molecule is linear and has the arrangement OC⋯BrCl, with the Br atom forming the intermolecular bond to carbon. Values of the r_s type for the distances r(C⋯Br) and r(BrCl) have been derived and the limitations imposed on these by the small coordinate a_Br are considered. The effect of bond shrinkage resulting from isotopic substitution at Br indicates that the r_s value of a_Br is underestimated and it is concluded that there is probably only a small increase in r(BrCl) on formation of the complex. An interpretation of the χ_aa(X) values indicates that the electric charge distribution in BrCl is also only slightly perturbed.