GROUND-STATE SPLITTING OF S-STATE ION CM3+ IN LACL3

We report optical-spectroscopic studies of the ground-state splitting of the nominal S-state ion Cm3+ in LaCl3. A total splitting of 1.97 +/- 0.05 cm-1 for the 8.S7/2 ground state of this system has been measured for the first time. Both electric and magnetic dipole transitions were observed. Energy levels of all four Kramers doublets of the 8S7/2 manifold were resolved by means of the site-selective excitation ana emission spectra of 8S7/2 <--> 6D7/2 and 8S7/2 <--> 6P5/2 transitions. Our results show that the lowest component of the ground manifold is a mu = 5/2 state dominated by M = \+/- 7/2] in contrast to a previously reported mu = 1/2 state. The crystal-field model, established through analyzing optical spectra of the excited states, predicts a ground-state splitting with the right ordering but greater magnitude. In comparison with the lanthanide S-state ion Gd3+, much stronger spin-orbit coupling and reduced electrostatic interaction in concert with greater crystal field interaction significantly influence the characteristics of the ground state of the actinide S-state ion. Contributions from within the 5f7 configuration account for most of the observed splitting.