Sum rules and spectral patterns of dichroism in inner-shell photoelectron spectra

Abstract

A theoretical description of dichroism in the photoelectron spectra of atoms polarized in different directions is presented. It is based on the general expression for the photoelectron angular distribution written in LSJ approximation. We show that, for photon energies far above threshold, the spectral distribution of dichroism in the photoelectron spectrum in most cases does not depend on the photoionization dynamics; for atoms with S symmetry, simple spectral patterns are obtained. Useful sum rules are given for the dichroism integrated over groups of photoelectron multiplet lines. Recent experimental data on magnetic dichroism and linear dichroism in the nonresonant inner-shell spectra of Cr (3p shell͒, Eu (4f shell͒, and Fe (3p shell͒ are analyzed. An outlook is given on the dichroism in the region of autoionization resonances. ͓S1050-2947͑99͒10808-4͔

Core-valence interactions in Cr and Fe2pphotoemission

“…14,16 In order to compare the magnetic dichroism, the thin film must be magnetized and the free atoms must be oriented ͑the magnetic sublevels m J of the Hund's rule ground state must be populated asymmetrically͒. [17][18][19][20] A. Cr 2p photoemission So far only the 2p photoemission spectra of a magnetized Cr surface layer on 12 ML Fe/ Cr/ W͑110͒ have been compared to the spectra of free laser-oriented Cr atoms. 17 The spectra and the magnetic dichroism based on a single configuration approximation ͑Cr + 2p 5 3d 5 4s͒ is well reproduced by Hartree-Fock calculations in intermediate coupling.…”

“…The resulting coefficients B k 0 kk ␥ contain the many-electron dipole matrix elements ͗␥ f J f , ⑀lj : JʈDʈ␥ 0 , J 0 ͘ and describe the dynamics of the photoionization process. 18 For a qualitative discussion it is instructive to consider the resulting dipole amplitudes within a pure coupling approximation. 18,19 In deep core-level photoemission the spin-orbit splitting of the core hole dominates the photoemission spectrum and therefore the jK or jj coupling approximations are appropriate.…”

Linear magnetic and alignment dichroism in Auger–photoelectron coincidence spectroscopy

“…Linear alignment dichroism (LAD) is the difference between cross sections for two perpendicular atomic alignments and for linearly polarized ionizing radiation [27].…”

“…Linear magnetic dichroism in angular distribution (LMD) 5 is defined as the difference between the cross sections for two directions of the atomic orientation antiparallel to each other when the target is ionized by means of linearly polarized synchrotron radiation [27,36].…”

“…Widespread investigations of magnetic circular dichroism in photoemission from solids are a good example of application of electron spectroscopy of polarized targets to studying the magnetic properties of solids (see, for example, [25] and references therein). In the gas phase, moreover, experiments with polarized targets provide important information about the electronic structure and correlations in atoms (see, for example, [26][27][28] and references therein) including complete information about the photoionization amplitudes (complete experiment) [29][30][31]. Although coincidence measurements from polarized targets are more difficult than conventional single-electron detection, such experiments are quite feasible with modern synchrotron radiation sources and modern equipment [32].…”