Combining high-resolution photoelectron spectroscopy and laser polarization for a study of the 4f and 5p photoionization of atomic thulium

The 4f and 5p subvalence photoionization of atomic Tm has been investigated by combining high-resolution photoelectron spectroscopy and dichroism measurements of the laser-polarized atoms. The experimental results are compared to Hartree–Fock calculations. The Tm 5p photoelectron spectrum is dominated by spin–orbit splitting whereas mixing of the final ionic states strongly influences the Tm 4f photoionization. Intermediate coupling is appropriate for the explanation of the complex Tm 4f multiplet structure, though some lines are well described within LS coupling. This suggests a partial breakdown of the LS -coupling approximation for Tm 4f photoionization. In comparison to the corresponding spectra of Eu the Tm spectra are much less affected by the admixture of 6s5d and 5d 2 valence electron configurations.