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

Accurate values have been obtained for the electric dipole (mu) and quadrupole (Theta) moment and the dipole polarizability (alpha(alpha beta)) of CS, SiO and SIS from finite-field many-body perturbation theory and coupled cluster calculations. For the ground state of the dipole moment we have obtained mu/e a(o) = 0.7903 (CS), -1.1843 (SiO) and -0.6124 (SIS) and for the quadrupole 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 quadrupole moment of CS, SiO and SiS. Our best values for the mean dipole polarizability 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 dipole 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 Delta 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).