Inter- and intramolecular electron transfer in the complex OC center dot center dot center dot ICl determined from iodine and chlorine nuclear quadrupole hyperfine structure in its rotational spectrum

The ground-state rotational spectra of three isotopomers (OC)-C-12 ... (ICl )-Cl-35, (OC)-C-12 ... (ICl)-Cl-37 and (OC)-C-13 ... (ICl)-Cl-35 of a linea r (or quasi-linear) complex formed by carbon monoxide and iodine monochlori de were observed by using a pulsed-nozzle, Fourier transform microwave spec trometer. The spectroscopic constants B-0, D-J, chi(aa)(I), chi(aa)(Cl) and M-bb(I) were determined for each isotopomer. Simple models were used to in terpret the spectroscopic constants to give details of the geometry, bindin g strength and electric charge redistribution in OC ... ICl. It was conclud ed that the nuclei lie in the order OC ... ICl with the distance r(C ... I) = 3.011(1) Angstrom, that the quadratic intermolecular stretching force co nstant k(sigma) = 8.00(3) N m(-1), and that, when CO achieves its equilibri um position in the complex, the changes in the iodine and chlorine nuclear quadrupole coupling constants of ICl are consistent with the transfer of a fraction delta(1) = 0.025(2) of an electronic charge from C to I and an int ramolecular transfer of a fraction delta(2) = 0.048(2) from I to Cl. A comp arison of the r(C ... X), k(sigma) and delta(2) values for the series of co mplexes OC ... XY, where XY = ClF, Cl-2, BrCl, Br-2 and ICl is presented. T he order of k(sigma) is ICl > ClF > BrCl > Br-2 > Cl-2, while the order of delta(2) is Cl-2 similar to ClF < Br-2 similar to BrCl < ICl. It is deduced that ICl is 'snub-nosed', i.e. the I atom has a smaller van der Waals radi us along the ICl internuclear axis than perpendicular to it.