Theory of polarization-averaged core-level molecular-frame photoelectron angular distributions: I. A full-potential method and its application to dissociating carbon monoxide dication

Abstract

We present a theoretical study of the polarization-averaged molecular-frame photoelectron angular distributions (PA-MFPADs) emitted from the 1s orbital of oxygen atoms of dissociating dicationic carbon monoxide CO2+. Due to the polarization average, the contribution of the direct wave of the photoelectron, which represents the largest contribution to the MFPADs, is removed, so that the PA-MFPADs clearly show the details of the scattering image of the photoelectron. As a result, it is necessary to employ an accurate theory for the theoretical analysis of the continuum state. In this study, we apply a full-potential multiple scattering theory, where the space is partitioned into Voronoi polyhedra and truncated spheres, to take into account the electron charge density outside the physical atomic spheres. We do not use the spherical harmonic expansion of the cell shape functions to avoid divergence problems. The potentials in the scattering cells are computed using the multiconfigurational second-order perturbation theory restricted active space method to take into account the influence of the core hole in the electron charge density in the final state, so that a realistic relaxation can be achieved. We show that the full-potential treatment plays an important role in the PA-MFPADs at a photoelectron kinetic energy of 100 eV. In contrast, the PA-MFPADs are not sensitive to any type of major excited states in the Auger final state. We also study the dynamics of the CO2+ dissociation. We find that the PA-MFPADs dramatically change their shape as a function of the C–O bond length.

Theory of polarization-averaged core-level molecular-frame photoelectron angular distributions: III. New formula for p- and s-wave interference analogous to Young’s double-slit experiment for core-level photoemission from hetero-diatomic molecules

“…The key difference between them is that Young's double-slit experiment represents the interference of two spherical s-waves, while the O 1s PA-MFPADs we are interested in consists in the interference between one p-wave, which is the direct wave emitted by the atom that absorbs an X-ray photon, and the wave scattered by the neighboring atom, which may be approximated by a s-wave. Using Multiple Scattering theory, we derive a new formula for the p-s wave interference in the PA-MFPADs, analogous to Young's formula for the s-s wave interference, and further examine the validity of this new formula, by applying it to the PA-MFPADs of dissociating CO 2+ calculated within the FPMS theory [25]. We also discuss the issue of applying the original Young's formula to the analysis of PA-MFPADs.…”

High-Energy Molecular-Frame Photoelectron Angular Distributions: A Molecular Bond-Length Ruler

“…To establish MFPAD measurements as a routinely usable tool for molecular structure imaging, however, an important ingredient is still missing, which is a method to extract the molecular structure directly from the measured MFPAD without the need of a full theoretical modeling of the photoemission process. So far, concepts proposed for achieving this goal focus on polarization-averaged MFPADs (see, e.g., [17] and references therein), and rely on two prerequisites: Firstly, at sufficiently high photoelectron kinetic energies for which a single-scattering approximation is valid (say, above 70 eV), forward-scattering peaks observable in polarization-averaged MFPADs coincide with the relative location (from the point of view of the emitter atom) of neighboring atoms [18,19]. Secondly, the molecularframe interference pattern caused by the direct and scattered photoelectron waves can be correlated to the distance between the emitter and the scatterers [20,21].…”

“…We assume that CP-MFPADs are measured in the polarization plane of the circular light and employ the electric-dipole, single-channel, and single-scattering approximations using a site T -matrix expansion [27,28]. In this case, the CP-MFPAD as a function of photoelectron emission vector, k, is given by the following form [17,21]:…”

An investigation of photoelectron angular distributions and circular dichroism of chiral molecules

“…Nevertheless, the node tends to be filled at intermediate angles (panel b and c), suggesting a more complex interpretation. The other features in the angular distribution emerge from the aforementioned scattering on the molecular potential, and from the effect of relevant dipole selection rules [92].…”

“…For the K-shell electrons, the MFPAD often shows a reminiscence of a dipolar emission pattern with respect to the photon polarisation direction [92]; other more meaningful features in the distribution to probe the molecular structure are emerging mainly from the scattering on the molecular potential (see chapter 3.1).…”