Spin-orbit and spin-spin couplings in He-2 and He-2(-)

The spin-orbit and the spin-spin coupling constants of the (4)Pi(g) state o f the He-2(-) ion, of the parent a(3)Sigma(u)(+), and of the b(3)Pi(g) stat es of He-2 have been evaluated by a multireference configuration interactio n method. The theoretical spin-spin splittings of the a(3)Sigma(u)(+) state and the R-dependent spin-spin function are found to be in excellent agreem ent with experiment, with deviations in the range of a few MHz. The theoret ical spin-orbit constants and splittings of the b(3)Pi(g) state are larger than the experimental values by about 370 MHz. The spinorbit coupling const ant of the (4)Pi(g) state of He-2(-) is estimated to be three times smaller than in the b(3)Pi(g) state, but one of the intramultiplet off-diagonal sp in-spin interactions is predicted to give a large contribution to the fine structure of the metastable ion. The theoretical fine structure constants f or the He-2(-) ion are expected to aid future spectroscopic investigations of the fine structure splittings of the negative ion.