Subshell photoionization of Xe between 40 and 1000 eV

Abstract

Partial cross sections and angular-distribution asymmetry parameters were measured for subshell photoionization of xenon for photon energies between 40 and 1000 eV. These large-scale measurements show that the pronounced interchannel coupling between the valence and the 4d electrons persists beyond the 4d shape resonance in the subsequent Cooper-minimum region. Multielectron processes associated with 4d and 4p photoemission were measured directly for the first time over a broader energy range covering the near-threshold behavior up to the sudden limit. Comparing our experimental results with calculations based on the single-particle model shows that this theory, which fails to describe the intermediate energy range even qualitatively for the valence electrons, gives partial cross sections in reasonable agreement with experiment at higher photon energies, particularly beyond the 3d threshold. The same result is shown by the angular-distribution asymmetry parameter P, except for the photoionization of the "4p" subshell which resembles more the behavior of a 4d electron, corroborating the theoretical assumptions of core-hole fluctuations between these two subshells. In the shape resonance region the presented 4d partial cross sections are in reasonable agreement with theoretical results obtained recently by many-body perturbation theory.

Conditions for extracting photoionization cross sections from laser-induced high-order-harmonic spectra

“…By comparing the measured high-orderharmonic generation (HHG) spectra of Kr and Xe atoms generated by intense 1.8-μm lasers and assuming that the photoionization cross section (PICS) of Kr is known, they deduced the differential PICS of Xe from the laser-generated HHG spectra. The deduced PICS reveals the well-known strong peak around 100 eV (photon energy), in good agreement with the 5p partial PICS that has been previously measured with synchrotron radiation light sources [2]. In the parlance of photoionization, this enhancement is caused by the so-called intershell coupling [3] with photoionization from the 4d shell of Xe, which is a specific form of the many-electron correlation effect [4].…”

Theory of multiple ionization of xenon under strong XUV radiation and the role of the giant resonance

“…It turns out, however, that such terms do not affect the results appreciably, because the pulse duration is longer than the relevant lifetimes [6].…”

“…This type of single-photon resonance has been studied, theoretically, as well as experimentally, quite extensively over the last few decades [6,7,8,9]. The magnitude of this feature is unusually large in Xenon, due to the double well shape of the potential and the strong localization of the continuum f-wave in the inner well at the resonance energy [7,10,11].…”

“…theoretical interpretation [5], in so far as the dependence of the ionic species on laser intensity is concerned, up to about Xe 15+ , has shown that the underlying mechanism is indeed compatible with sequential ionization; beginning with the single-photon ejection of a 4d electron and the subsequent Auger process producing (with known branching ratios) one or two more electrons [6]. As a consequence of the relevant branching ratios, the most abundant species, throughout the intensity range covered in the experiments [2,3], is Xe 2+ , followed by Xe 3+ .…”

“…while the values of the cross sections, in units cm For single-photon processes (up to Xe 7+ ), the cross sections have been taken from [6,8,9], as well as checked through independent calculation using Cowan's code (http://aphysics2.lanl.gov/cgi-bin/ION/runlanl08d.pl ). Multiphoton cross sections have been obtained mainly through scaling [21], while some 2-photon cross sections have also been calculated through a truncated summation.…”