Abstract: The absorption spectra of pseudo (ψ) trigonal planar Sm(η5-C5Me4H)3 (1) and La(η5-C5Me4H)3 (2) in KBr pellets have been measured at room temperature and 77K, respectively. Additionally, the linear dichroism spectra of σ and π type of an oriented single crystal of 1 have been recorded at ambient temperature. The observed polarization properties of the f–f transitions allowed the assignment of the transitions. The free parameters of a phenomenological Hamiltonian were fitted to the energies of the assigned terminal levels, leading to a reduced r.m.s. deviation of 19.1cm−1 for 19 assignments. On the basis of these phenomenological CF parameters, the global CF strength experienced by the Sm3+ central ion was estimated, and seems to be the largest one ever encountered in samarium(III) chemistry. The obtained Slater parameter F 2 and the spin–orbit coupling parameter ζ 4f allow the insertion of compound 1 into empirical nephelauxetic and relativistic nephelauxetic series, respectively. On the basis of these models, complex 1 turns out to be the most covalent SmIII compound found to date. The experimentally-based non-relativistic molecular orbital scheme (in the f range) of complex 1 was determined and compared with the results of a previous Xα-SW calculation on the ψ trigonal planar model compound Sm(η5-C5H5)3. [Copyright &y& Elsevier]