Ab initio based configuration interaction study of the electronic spectrumof GeS

The electronic spectrum of GeS has been studied by using ab initio based mu ltireference configuration interaction calculations which include relativis tic effective core potentials of Ge and S atoms. Potential-energy curves of 27 Lambda -S states of GeS correlating with two dissociation limits have b een computed. Spectroscopic constants of bound states are computed and comp ared with some of the observed states such as X(1)Sigma (+), a(3)Sigma (+), b(3)Pi, A(1)Pi, and E(1)Sigma (+). The ground state of GeS is composed of two dominant configurations:...sigma (2)pi (4) and ...sigma (2)pi (3)pi* wi th r(e) = 2.039 Angstrom and omega (e) = 549 cm(-1), which compare well wit h the observed values. The ground-state dissociation energy of GeS is also estimated. The observed E state is assigned to 2(1)Sigma (+). Effects of th e spin-orbit coupling have been explored on 18 Lambda -S states all of whic h converge with the lowest dissociation limit P-3(g)(Ge) + P-3(g)(S). Poten tial-energy curves of all 50 Omega states arising from the spinorbit intera ctions in these Lambda -S states are computed. Transition probabilities of some dipole-allowed transitions are estimated. Transitions such as b(3)Pi ( 0+)-X(1)Sigma (+)(0+) and b(3)Pi (1)-X(1)Sigma (+)(0+) which are analogous to the Cameron bands of the isovalent CO are investigated. The observed a(3 )Sigma (+)(1)-X(1)Sigma (+)(0+) transition of GeS is also studied. Radiativ e lifetimes of A(1)Pi (1), E(1)Sigma (+)(0+), a(3)Sigma (+)(1), b3 Pi (0+), b(3)Pi (1), and some other components are estimated.