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

Recent studies indicate that several bound states exist for some negat ive ions of the lanthanides. In this work we demonstrate that the seco nd member of the actinide series, Th, also possesses multiple negative ion states below its ground state, consistent with the relatively hig h yield observed in the laboratory. Our valence space relativistic-con figuration-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 affinitie s (EA) of 0.365 and 0.189 eV, respectively. We also expect certain wea ker 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=+ (-) correspond s to even (odd) parity states.