Geometry, strength of binding and Br2 charge redistribution in the complex OC•••Br2 determined by rotational spectroscopy

The ground-state rotational spectra of the six isotopomers (OC)-O-16-C-12 ...(BrBr)-Br-79-Br-79, (OC)-O-16-C-12 ...(BrBr)-Br-81-Br-79, (OC)-O-16-C-12 ...(BrBr)-Br-81-Br-81, (OC)-O-16-C-12 ...(BrB)-Br-79-B-81, (OC)-O-16-C-13 ...(BrB)-Br-79-B-79, (OC)-O-16-C-13 ...(BrBr)-Br-81-Br-79, were observed by pulsed-nozzle, Fourier-transform microwave spectroscopy. The spectroscopic constants B-0, D-J, chi(aa)(Br-i), chi(aa)(Br-o), M-bb(Br-i) and M-bb(Br-o), where i = inner and o = outer, were determined for each isotopomer. The complex is linear, with the weak bond between the C atom of CO and Br The rotational constants were used to determine the distance r(C ... Br-i) = 3.1058 Angstrom and to show that the Br-Br bond lengthens by similar to 0.005-0.01 Angstrom on complex formation. The intermolecular stretching force constant k(sigma) = 5.0 N m(-1) was obtained from DJ and the Br nuclear quadrupole coupling constants were interpreted to reveal that a fraction delta = 0.02 of an electronic charge is transferred from Br-i to Br-o when Br-2 is subsumed into the complex. Properties of the two series OC ... XY and H3N ... XY, where XY = Cl-2, Br-2 and BrCl, are compared.