Spin-polarized and site-selective X-ray absorption. Demonstration with Fe porphyrins and Kβ detection

High-spin and low-spin Fe(III) porphyrins were studied by high resolution X-ray fluorescence and fluorescence-detected X-ray absorption spectroscopy using synchrotron radiation. The high-spin Kβ spectrum is split into a main peak (Kβ1,3) and a satellite (Kβ′) at 15 eV lower energy. The low-spin Kβ1,3 peak shifted ≈ 0.7 eV to lower energy, and the Kβ′ feature is almost unobservable. Ligand field multiplet calculations show that spin-up (5A1) and spin-down (7A1) states are separated for the high-spin spectrum. Spin polarization of the Kβ-detected absorption was demonstrated by enhancement or elimination of the 1s→3d transition, depending on the Kβ region used for detection.