Electronic spectrum of silicon monosulfide: Configuration interaction study

Ab initio based configuration interaction calculations using relativistic effective core potentials and compatible basis sets have been performed to study the electronic spectrum of the silicon monosulfide molecule. Potential energy curves of low-lying states of SiS have been computed. Spectroscopic properties of many observed states such as X(1)Sigma(+), a(3)Sigma(+), d(3)Delta, b(3)Pi, C(1)Sigma(-), e(3)Sigma(-), D(1)Delta, A(1)Pi, and E(1)Sigma(+) up to 42000 cm(-1) of energy have been calculated and compared. The ground state of SiS is represented mainly by ...pi(4) (74%) and ...pi(3)pi(*) (12%) configurations with r(e) = 1.957 Angstrom (3.7 a(0)) and omega(e) = 733 cm(-1), which compare well with the observed values. The dissociation energies of the ground and excited states have been estimated. All 18 A-S states correlating with the lowest asymptote have been allowed to mix through the spin-orbit coupling. Effects of spin-orbit interactions on the potential energy curves and spectroscopic properties of the low-lying states of SiS are studied. Dipole-allowed transitions such as E-X and A-X are found to be strong. Several spin-forbidden weak transitions are also noted. The radiative lifetimes of many upper states are estimated. The E(1)Sigma(0+)(+) and A(1)Pi(1) states are predicted to be short-lived with radiative lifetimes of about 10.2 and 103 ns, respectively.