Hyperfine and nuclear quadrupole coupling in chlorine and fluorine dioxides

The hyperfine and nuclear quadrupole coupling tensors have been calculated for the two chlorine dioxide isomers OClO and ClOO and for fluorine dioxide FOO. The coupled-cluster singles and doubles (CCSD) approach with a perturbative treatment of triple excitations [CCSD(T)] has been used and basis saturation has been investigated. For the symmetric isomer OClO close agreement is obtained with the accurate and detailed experimental data. For FOO a geometry optimization as well as a comparison of calculated and experimental hyperfine coupling tensors suggest a shorter F–O bond length than that obtained experimentally. For the isomer ClOO, calculations have been carried out at the theoretical equilibrium geometry determined by Peterson and Werner and at the geometry proposed by Byberg for the matrix isolated molecule. The hyperfine coupling tensors obtained at these two geometries are substantially different, but the estimated accuracy of the calculations is not high enough to allow a determination of the geometry of ClOO from the hyperfine data.