Geometry-dependent analysis of 2p3d- and 2p3s-partial fluorescence yield spectra for high-spin 3d⁵ systems

Geometry dependences of partial fluorescence yield (PFY) spectra at the L_2,3-edge of 3d transition metals are discussed theoretically and experimentally for high-spin 3d⁵ systems in O_h and T_d point symmetries. Firstly, linear polarized light's propagation direction selection rules for a two-photon process are applied to 2p3d-PFY spectroscopy. Then, the 2p3d-PFY spectra were analyzed by comparison with spectra obtained as partial integration of 2p3d-resonant inelastic X-ray scattering (RIXS) signals, utilizing the relationship between PFY and RIXS spectroscopies: the former is an integration of yield of emitted light at each excitation energy, and the latter is a dispersion of emitted light as a function of emission energy at each excitation energy. Thus, a PFY spectrum can be divided into super PFY (sPFY) spectra using partial integrations of signals on a RIXS map, such as sPFY spectra from elastic and inelastic signals. It is suggested that the origin of the large deviation of 2p3d-PFY spectral shape in a linear-horizontal geometry from a true X-ray absorption spectrum is due to the lack of elastic signals, i.e., the lack of signals emitted when the system returns to its ground state. Contrary to a 2p3d-PFY spectrum, a 2p3s-PFY spectrum is often assumed to have a one-to-one correspondence with true XAS; however, 2p3s-PFY spectroscopy is also a two-photon process that abides by the propagation direction selection rules. We will show theoretically that 2p3s-PFY spectral shapes show a geometry dependence and offer a way to obtain a true X-ray absorption structure from a combination of 2p3s-PFY spectra in linear-vertical and linear-horizontal geometries.