Energy dependence of the outer core-level multiplet structures in atomic Mn and Mn-containing compounds

We consider the energy dependence of the Mn 3s and 3p multiplets from gas-phase atomic Mn and crystalline ${\mathrm{MnF}}_2$ and ${\mathrm{KMnF}}_3$ over the range from x-ray photoelectron spectroscopy (XPS) energies down to energies near threshold. First comparing atomic and solid-state spectra for these multiplets permits concluding that the splittings in the compounds ${\mathrm{MnF}}_2$, MnO, and ${\mathrm{Cd}}_{0.3}$ ${\mathrm{Mn}}_{0.7}$Te are highly atomic in character, with no significant effects due to extra-atomic screening. Measuring the energy dependence for atomic Mn, ${\mathrm{MnF}}_2$, and ${\mathrm{KMnF}}_3$ then shows for both the 3s and 3p multiplets that there is a decrease in the intensities of the higher-binding-energy quintet states relative to those of the corresponding septet states as the excitation energy is lowered. This effect on the quintet:septet branching ratios is also found to extend to rather high energies, with the ratios at the XPS limit of ≊1400 eV above threshold being approximately 25–30 % greater than those at ≊200 eV above threshold. We show that this energy-dependent final-state branching ratio is not due simply to spin-dependent dipole matrix elements as derived from single-configuration Hartree-Fock calculations. We suggest that this effect is caused by the sudden-to-adiabatic transition, which at lower energies favors the exchange-stabilized septet states that are the ground states of the ions formed. However, two prior theoretical models for such sudden-to-adiabatic intensity changes [Stohr, Jaeger, and Rehr, Phys. Rev. Lett. 51, 821 (1983) and Thomas, Phys. Rev. Lett. 54, 182 (1985)] were not found to describe our results well, particularly in the extension of the effect to higher energies. We consider qualitatively a configuration-interaction model with quintet-septet interchannel coupling that may better describe these effects and form the basis for more quantitative calculations.