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 8𝒮7/2 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 and 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 μ=5/2 state dominated by M=‖±7/2〉 in contrast to a previously reported μ=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.