Piter S. Miedema

2p x-ray absorption of iron-phthalocyanine

3d transition metal ions, like Fe(II) in a planar organic environment are subject to the details of the ligand coordination. In this study the 3d orbital splitting in planar D4h symmetry is investigated for Fe(II) using the charge transfer multiplet program. By variation of the 10Dq, Ds and Dt crystal field parameters, the 3d orbitals split differently giving rise to different spin multiplicity. The relative occupations of the 3d orbitals yield a range of ground states. Experimental x-ray absorption spectra of FePc powder are compared with theoretical simulations, resulting in the spin ground state of the Fe(II) ion being 3E.

First principles multiplet calculations of the calcium L-2,L-3 x-ray absorption spectra of CaO and CaF2

First principles calculations are performed for the interpretation of the L₂,₃ x-ray absorption spectrum of calcium oxide and calcium fluoride. The first principles calculations are based on configuration interaction (CI) calculations using fully relativistic molecular spinors. The first principles results are compared to experimental data and also to calculations based on a semi-empirical crystal field multiplet model and also on a multichannel multiple scattering method. We show that the CI calculations show good agreement with experiment, both for bulk and for surface experiments. The remaining differences with experiment and between the theoretical models are discussed in detail.

The accuracy of the spin sum rule in XMCD

The effective spin sum rule is reviewed with a detailed analysis of the various sources for errors and deviations of this widely used X-ray Magnetic Circular Dichroism (XMCD) tool. The simulations confirm that the final state effects of the core level spin-orbit coupling and the core-valence exchange interactions (multiplet effects) are linearly related with the effective spin sum rule error. Within the ligand field multiplet approach, we have analyzed these effects, in combination with the interactions affecting the magnetic ground state, including the crystal field strength and the 3d spin-orbit coupling. We find that for the late transition metal systems, the error in the effective spin moment is between 5 and 10%. Because of the potentially large value, the spin moment can not reliably be determined for all systems other than Ni. The error for 3d 4 systems is very large, implying that, without further information, the derived effective spin sum rule values for 3d 4 systems have no meaning.

X-ray spectroscopy with variable line spacing based on reflection zone plate optics

X-ray spectroscopy is a method, ideally suited for investigating the electronic structure of matter, which has been enabled by the rapid developments in light sources and instruments. The x-ray fluorescence lines of life-relevant elements such as carbon, nitrogen, and oxygen are located in the soft x-ray regime and call for suitable spectrometer devices. In this Letter, we present a high-resolution spectrum of liquid water, recorded with a soft x-ray spectrometer based on a reflection zone plate (RZP) design. The RZP-based spectrometer with meridional variation of line space density from 2953 to 3757xa0l/mm offers extremely high detection efficiency and, at the same time, medium energy resolution. We can reproduce the well-known splitting of liquid water in the lone pair regime with 10xa0s acquisition time.

Total 3s Emission Yield as Bulk-Sensitive Probe for a True Soft X-ray Absorption Spectrum?

The detection of the true soft X-ray absorption typically needs specially prepared submicrometer thin samples for transmission measurements. Bulk experiments instead have to rely on yield methods, for example, electron yield with limitations for insulating samples, sensitivity to applied fields, and with limited bulk sensitivity. Fluorescence yield methods instead do not have those limitations but have been found to deviate, in general, from the absorption spectrum. We demonstrate that restricting the detection to the 3s fluorescence channel (with the detector at a special angle where all polarizations contribute equally) restores the true X-ray absorption spectrum for all 3d-metal L2,3 edges. These theoretically derived results are rationalized by the lack of 3s-3d interaction in the core-excited state. Comparing X-ray absorption versus 3s-PFY for arbitrary detection geometries for both linear and circular polarized light, deviations appear that can become as large as 15%.