Using K Pre-Edge XAS to Follow Spin Transition in Fe³⁺

The following tutorial shows how changes in the X-ray absorption spectrum at the K pre-edge, resulting from 1s to 3d transitions, can be used to track the spin state of Fe³⁺ compounds.

1. Write down the electronic configuration of Fe³⁺. Show that there are two ways to fill the 3d orbitals, leading to a high spin (S = 5/2) and a low spin ground state (S = 1/2).

2. Run two K pre-edge calculations for Fe³⁺ in an octahedral crystal field, one with 10Dq set to 2.0 eV and 3.3 eV. What differences do you observe between the two spectra? Based on the two calculations what can you say about the spin state of Fe³⁺ in the experimental spectrum below.

Westre et al., J. Am. Chem. Soc., 1997, 119 (27), 6297–6314.

3. Change the 10Dq value from 2.6 to 3.6 eV in steps of 0.1 eV. At what value do you observe the spin transition?

4. Is it possible to induce a low spin to high spin transition by changing the scaling factors of the Slater integrals while keeping the 10Dq set to 3.3 eV?