ELECTRON-AFFINITIES OF OPPOSITE-PARITY BOUND-STATES IN TH- - RELATIVISTIC-CONFIGURATION-INTERACTION STUDIES

Recent studies indicate that several bound states exist for some negative ions of the lanthanides. In this work we demonstrate that the second member of the actinide series, Th, also possesses multiple negative ion states below its ground state, consistent with the relatively high yield observed in the laboratory. Our valence space relativistic-configuration-interaction calculations predict the strongest bindings for Th- 6d(2)7s(2)7p J=2.5 and Th- 6d(3)7s2 J=1.5 with electron affinities (EA) of 0.365 and 0.189 eV, respectively. We also expect certain weaker candidates to exist with (J(pi), EA (eV)): (0.5(-),0.088), (1.5(-),0.075), (3.5(-),0.042), and (2.5(+),0.056), where pi=+ (-) corresponds to even (odd) parity states.