Photo-double-ionization of Mg studied by electron-electron-coincidence experiments

Abstract

The photo-double-ionization (PDI) of Mg to the Mg 2+ (3s −2) state has been studied by photoelectronphotoelectron-coincidence experiments at a photon energy corresponding to the excitation of the 2p→3d resonance. The equal energy sharing (E 1 = E 2 = 16.4 eV) as well as the complementary unequal energy (E 1 ↔E 2 = 10.4↔22.4 eV) sharing kinematics have been investigated. From the experimental results without any approximation the symmetrized gerade and ungerade amplitudes have been obtained. The experimental angular correlation patterns as well as the amplitudes are compared to CCC calculations in which the resonant process has been incorporated. The results confirm that the amplitudes of the photo-double-ionization carry the signature of the target radial wave function. The investigation of the triple differential cross sections has been then extended by simulations to a kinematics with the fixed detector at 90 o , which can not be studied experimentally by the present setup. These simulations shed light on results of previous measurements on alkaline-earth-metal atoms in this kinematics, which were not consistent with the common understanding of photo-double-ionization derived from He experiments.

Dissociation dynamics of the water dication following one-photon double ionization. I. Theory

“…The current state of the art for ab initio calculation of double photoionization amplitudes is to treat the dynamics of two active electrons completely while freezing the others in target atomic or molecular orbitals. Such calculations have only been carried out on atoms [38][39][40][41][70][71][72][73] to our knowledge, but in those cases surprisingly good agreement with experimental angular distributions of the ejected electrons was obtained. To calculate the TDCS for onephoton double ionization of water, we can make the same two-active-electron approximation, and use the computational methods involving a single center expansion and numerical grids that we have used previously in double photoionization calculations on H 2 [47][48][49][50].…”

Fully differential single-photon double photoionization of atomic magnesium

“…The TDCS plotted for the present results are absolute, with good agreement seen between the different gauges indicating a suitably converged description of the initial target state valence electrons within the frozen-core approximation. Experimental measurement points measured at Elettra [18] are also shown in each panel, as are the results from previous theoretical calculations: the time dependent close coupling (TDCC) results [19], convergent close coupling (CCC) calculations [18]. Following the comparison and discussion in Refs.…”

“…Following the comparison and discussion in Refs. [18] and [19], the non-resonant CCC calculation results are absolute while the resonant CCC calculation (employing a semi-empirical treatment to account for the resonance process populating the 3d state of the target) has been scaled by a factor of 3q 2 , where q is the Fano q parameter, taken here with a value of 50 [18]. The TDCC results are also absolute.…”

“…Most recently, theory and experiment have examined DPI from the valence shell of atomic magnesium, which has a neon-like core interacting with the 3s 2 outer electrons. Experimental measurements [17,18] of the triple differential cross section (TDCS), which measures the angular distributions of both electrons and their energy sharing above the double ionization threshold have been recently compared to theoretical calculations using the convergent close coupling (CCC) [18] and timedependent close coupling (TDCC) [19] methods at a photon energy of 55.49 eV. This energy is resonant with the state resulting from promotion of a 2p → 3d electron embedded in the double continuum.…”

“…A formulation that can fully take into account the dynamics of this resonant process currently lies beyond any theoretical treatment for examination of quasi-two electron targets. Nevertheless, there have been comparisons of the experimental results undertaken with theoretical descriptions at this photon energy approximated by non-resonant ab initio calculations that feature only two-active electrons [18,19] or by a semi-empirical accounting of the Fano profile of the resonant transition [18].…”