Direct Double Photoionization Involving Inner and Outer Electrons: First Experimental Determination and Many-Body Calculations of an Absolute Cross Section

Abstract

Using synchrotron radiation, we have determined the absolute cross section for double photoionization involving the 2p and 3s electrons in atomic sodium. %e have also calculated this cross section in the many-body perturbation theory approximation.Our experimental and theoretical results are in good agreement one with each other and represents the first absolute determination of a double photoionization cross section in the case where the two electrons belong to two different shells.PACS numbers: 32.80. Hd, 32.80.Fb In this Letter, we present the results of the first experimental determination of an absolute double photoionization cross section for the direct emission into the continuum of two electrons belonging to two different shells. These measurements were performed for simultaneous photoionization of 2p and 3s electrons in sodium atoms. We also present calculations of the double photoionization cross section of Na (2p3s kik2) for photon energy from 50 to 250 eV, using many-body perturbation theory (MBPT).Double photoionization (DPI) in the outer shell of atoms has long attracted considerable interest, because it provides a sensitive test for the importance of electronelectron correlation effects. Earlier work on the rare gases [1 -4] revealed that the shakeoff theory, describing DPI as the result of monopole transitions resulting from relaxation of the hole state produced in the outer shell, was unable to account for most of the DPI intensity. MBPT was used at that time to calculate DPI cross sections in neon [5 -7], helium [8], and argon [7]. Agreement with the first experimental data available was reasonably good, especially for helium [9]. Most recently, DPI has been extensively studied in the outer shell of the rare gases [10 -18], owing to the increased performance of synchrotron radiation (SR) sources. In the measurements of the energy dependence of the branching ratio between double and single photoionization cross sections, considerable attention was given to the threshold [10-12] and high energy [13 -15] behaviors of DPI. Some data have also been obtained in the study [16 -18] of the energy and angle-resolved DPI process. Parallel to this experimental activity, progress has also been made in theoretical calculations of DPI cross section for helium [19 -22] and for argon [23].When the primary vacancy is produced in an inner atomic subshell, doubly charged ions can result from two different mechanisms.In the one-step DPI, a second electron is simultaneously ejected from the outer shell via correlation effects, namely [5 -8] core relaxation (CR), ground state correlations (GSC), and inelastic scattering (IS) of the photoelectron in collision with outer shell electrons while leaving the atom. CR and IS can be grouped into the category of final state correlations (FSC), although such a classification should be considered with some caution, as it has been shown that it is gauge dependent [19]. In the two-step process [24], the ejection of the first electron is followed by Auger decay of the singly c...

Double Rydberg States Formed in Stabilized Triple Electron Capture

“…The outgoing electron could also share the released energy with the third external electron ͑n 4 or 5͒, resulting in a two Rydberg electron bound state with high n, n 0 . Similar simultaneous two electron excitation has been observed in double photoionization experiments [18]. However, in present collisions, the excitation is in bound states instead of in the continuum.…”

Core-valence doubly ionized states: General aspects, examples, production mechanisms

“…Very recently, the first experimental determination of an absolute double photoionization cross section for the direct emission into the continuum of two electrons belonging to two different shells succeeded. 21 These measurements were performed for simultaneous photoionization of 2p ͑core͒ and 3s ͑valence͒ electrons in sodium atoms.…”

Experimental Investigation of Core-Valence Double Photoionization

“…Direct experimental observations of core-valence DPI are limited to a few cases involving, for example, the 2p core hole in Na [3] or the 4d hole in Xe [4]. Theoretical calculations have identified peculiar properties of core-valence doubly ionized states [5].…”