Near-UV excited-state absorption spectra obtained with a pulsed pump–probe technique were recorded in at 77 and at 8 K and revealed a detailed structure of the and optical transitions. These experimental results, together with those previously obtained at room temperature, are compared with the numerical predictions of a full calculation of the sublevels and of the electric dipole transitions toward these sublevels from different states of the configuration. The agreement is good, provided that the four adjustable parameters of the theory are taken as and Å. The level structure of the configuration of is shown to be dominated, as expected, by the crystal field coupling of the electron but also, to a noticeable extent, by the spin–orbit coupling of the electron and the Coulomb repulsion of both electrons. The former of these two interactions is somewhat more efficient than the latter in the low-energy part of the configuration, i.e., in the spectral region where the largest amount of experimental data is currently available.
© 2000 Optical Society of America