ROTATIONAL SPECTRUM OF THE GAS-PHASE DIMER OC...BRCL

The ground-state rotational spectra of the six isotopomers (OC)-O-16-C-12...(BrCl)-Br-79-Cl-35, (OC)-O-16-C-12...(BrCl)-Br-81-Cl-35 (OC)-O-16-C-12...(BrCl)-Br-79-Cl-37, (OC)-O-16-C-12...(BrCl)-Br-81-Cl-37, (OC)-O-16-C-13...(BrCl)-Br-79-Cl-35, and (OC)-O-16-C-13...(BrCl)-Br-81-Cl-35 of a dimer formed by carbon monoxide and bromine monochloride have been observed by pulsed-nozzle, Fourier-transform microwave spectroscopy. The rotational constant B(o), the centrifugal distortion constant D(j) and the halogen nuclear quadrupole coupling constants chi(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 chi(aa)(X) values indicates that the electric charge distribution in BrCl is also only slightly perturbed.