Double photoionization of excited1Sand3

Abstract

We present results for the photoionization of ground and excited S states of two-electron systems byx-ray photons. The method uses the asymptotic formulation of Dalgarno and Stewart [Proc. Phys. Soc. London 76, 49 (1960)] with highly correlated Frankowski-Pekeris -type wave functions for N 'S and N 'S initial states. The calculations show a smaller ratio of double-to-single photoionization R for triplet states due to the spatial antisymmetry of the wave function near the nucleus. We find an asymmetric population of photoion satellite states and provide expressions for the asymptotic single and total photoionization, and R as a function of nuclear charge. We also make predictions for the differential double photoionization cross sections in the extreme energy sharing case when one electron is ejected with zero energy.PACS number(s): 32.80.Fb, 32.30.Rj, 32.70.Cs I. INTRGDUCTIQNConsiderable attention has been given recently in experimental [1 -3] and theoretical [4 -8] studies to the double ionization of the ground state of helium by the absorption of a high-frequency photon. The double photoionization (DPI) of the other members of the helium sequence and of the metastable 2 S states of helium have also been investigated [5,9,10]. It has been established that the ratio of the double-to-single photoionization cross section tends to a constant at high frequencies. The asymptotic ratio can be calculated accurately in the acceleration form of the electric-dipole operator, provided that electron-electron correlation is adequately represented in the initial state wave function [11].In this paper, we employ fully correlated initial state wave functions for the ground and excited 'S and S states of helium to predict the asymptotic ratios for single and double photoionization.We use an extrapolation of the simultaneous excitation and ionization cross sections in the double-ionization limit to obtain the differential cross section for double photoionization in which one electron is ejected with zero energy. To explore further the role of electron-electron correlation, we investigate Electronic address: rcf@cfaitamp. harvard. edu tElectronic address: hrs@cfaitamp. harvard. edu the dependence of the ratios and cross sections on the nuclear charge Z. II. THKGRY A. Asymptotic formulationThe fundamental physical photoexcitation-ionization process quantity in the A'co+He(X ' S)~He+(ns)+e is the continuum dipole oscillator strength n ""=2co( (P"(r"r,)~X d~e(r, , r, ) ) (', where~and e are the respective energies of the photon and ionized electron in atomic units and R is the direction of linearly polarized light. %(r&, r2) represents a fully correlated initial state wave function, which is denoted by %(r"rz, r, )2for S states, and g"(r"r2) is the final state product wave function for a continuum electron and a hydrogenic s-state electron with principle quantum number n. The coordinates rj and r2 are the electronic distances from the nucleus, and r, 2 is the interelectronic distance. By Fourier transforming the acceleration form of ...

Nonrelativistic double photoeffect on lithium-like ions at high energies

“…The growing number of theoretical calculations has been recently devoted to the double photoeffect on excited metastable 2 1,3 S states of the helium isoelectronic sequence [4,5,6,7,8,9,10,11,12,13]. The problem is also of particular interest, because it is concerned with the study of inter-shell electron correlations.…”

Photoinduced K-shell hollow atoms

“…All energies are in eV. Because the shake-off asymptotic non-relativistic highenergy limit can be calculated quite accurately for the helium isoelectronic sequence and it is almost the same for neutral atoms and He-like ions [42,47], for R ∞ the values from Forrey et al [48] were used. For the knock-out probability P KO (E), the analytical form of the universal shape function for electron impact ionization of Hlike ions of Aichele et al [49] was adopted.…”

Double K-Vacancy Production by X-Ray Photoionization

“…In the high energy limit, final-state correlation is negligible and only the ground-state correlation needs to be accurately treated. Very accurate 1s 2 ground state wavefunctions can be constructed for He and He-like ions [8,9]. The results of those calculations provide reference values for experiments that measure R of many-electron targets under the assumption that interaction with outer-shell electrons is negligible.…”

“…3 along with results for other atoms [1,10,11,12]. For reference, the calculated asymptotic Z-scaling law of [8] is also shown. Except for the high-energy measurement on He [10], the measured ratios are significantly higher than the asymptotic limit, as expected.…”

“…High-energy-limit calculations [8,9] are interesting and useful, because they are considered to be asymptotically exact and provide reference values for experiments on atoms other than He. In the high energy limit, final-state correlation is negligible and only the ground-state correlation needs to be accurately treated.…”