ELECTRON CORRELATION AND RELATIVISTIC CONTRIBUTIONS TO MOLECULAR ELECTRIC PROPERTIES - DIPOLE AND QUADRUPOLE-MOMENTS OF CYANOGEN HALIDES

Polarized basis sets have been used for high level correlated calculations of dipole and quadrupole moments and dipole polarizabilities of cyanogen halides. The relativistic contributions to those properties have been accounted for within a quasirelativistic approach based on the Cowan-Griffin approximation. The calculated dipole moments (FCN, -2.196 D; ClCN, -2.869 D; BrCN, -3.187 D; ICN, -3.628 D) agree perfectly with the available experimental values. The quadrupole moments (in Buckingham) have been calculated for different isotopomers of cyanogen halides (FCN)-F-19-N-15, -3.907; (ClCN)-Cl-35-N-15, -3.933; (ClCN)-Cl-37-N-15, -4.112; (BrCN)-Br-79-N-15, -5.929; (BrCN)-Br-81-N-15, -6.002; (ICN)-I-127-N-15, -7.417) for the origin at the nuclear centre of mass. They can be used to narrow uncertainty of the experimental quadrupole moment data. The role of the electron correlation and relativistic contributions to electric properties of cyanogen halides is discussed. It has been found that only in the case of ICN is the relativistic contribution sizeable enough to modify noticeably the nonrelativistic results. The relativistic contributions to quadrupole moments are found to be more important than the corresponding corrections to dipole moments of cyanogen halides.