Electric dipole and quadrupole moment and dipole polarizability of CS, SiOand SiS

Accurate values have been obtained for the electric dipole (mu) and quadrup ole (Theta) moment and the dipole polarizability (alpha(alpha beta)) of CS, SiO and SIS from finite-field many-body perturbation theory and coupled cl uster calculations. For the ground state of the dipole moment we have obtai ned mu/e a(o) = 0.7903 (CS), -1.1843 (SiO) and -0.6124 (SIS) and for the qu adrupole moment Theta/e a(o)(2) = -1.85 (CS), -2.94 (SiO) and -0.37 (SiS). These values agree well with the available experimental data for the dipole moment. Discrepancies between theory and experiment are observed for the q uadrupole moment of CS, SiO and SiS. Our best values for the mean dipole po larizability of the isoelectronic CS and SiO are <(alpha)over bar>/e(2) a(o )(2) E-h(-1) = 28.87 (CS) and 29.67 (SiO). SiO is less anisotropic than CS, as Delta alpha/e(2) a(o)(2) E-h(-1) = 14.45 (CS) and 7.66 (SiO). The dipol e and quadrupole moments, the mean and the anisotropy of the polarizability of SiS at the MP4 level of theory vary around the equilibrium bond length R-e as mu(R)/e a(o) = -0.5658 - 0.6070 Delta R + 0.2997 Delta R-2 + 0.2316 Delta R -3 Theta(R)/e a(o)(2) = -0.42 + 2.37 Delta R - 0.62 Delta R-2 + 0.26 Delta R-3 <(alpha)over bar>(R)/e(2) a(o)(2) E-h(-1) = 50.10 + 15.67 Delta R + 3.68 De lta R-2 + 0.17 Delta R-3, Delta alpha(R)/e(2) a(o)(2) E-h(-1) = 27.23 + 26.00 Delta R + 10.02 Delta R -2 + 3.57 Delta R-3, with Delta R = (R - R-e)/a(o).