Ab initiocalculation of the whole set of He double-photoionization cross sections

Abstract

The double photoionization of He is investigated using the hyperspherical R matrix with semiclassical outgoing waves method. Triply, doubly, and singly differential, as well as fully integrated, cross sections are computed in a variety of geometrical and dynamical situations. The results are found to be in excellent agreement with absolute measurements both in shape and, more importantly, in magnitude. This demonstrates the robustness and accuracy of this ab initio method, which also provides a visualization of the formation of the various cross sections during the expansion of the system. This visualization reveals that, for very asymmetric energy sharings, the cross sections take their final form when the electrons are thousands of atomic units away from the ionic core, a distance where no other method is able to describe the double continuum wave function accurately.

Recoil-ion and electron momentum spectroscopy: reaction-microscopes

“…A detailed discussion goes beyond the scope of the present review; we refer the reader to (Briggs and Schmidt 2000). In general, very good agreement is found between the experimental data even on absolute scale and the most advanced theoretical approaches Kheifets and Bray 1998a;Kheifets and Bray 2000;Malegat et al 2000;Malegat et al 2002;Selles et al 2002;Pont and Shakeshaft 1995;Pont and Shakeshaft 1996a;Colgan et al 2001;Colgan and Pindzola 2002). At very high excess energies of eV 450 finally , one electron is found to leave fast, carrying away most of the photon energy and angular momentum.…”

Hyperspherical partial wave calculation for double photoionization of the helium atom at 20 eV excess energy

“…Results do not depend significantly on these. But for converged results in some situations, values of R ∞ , as in HRM-SOW calculation [9], are to be thousands of atomic units. Next we proceed for solutions over subdomains.…”

“…[9]). As regards the differential cross-sections, understanding of the results has much improved with the availability of results of some elaborate calculations like the time-dependent close coupling (TDCC) calculation of Colgan et al [7], the HRM-SOW calculation of Malegat et al and Selles et al [8,9] in addition to the earlier results ( [10,11,12,13]) and the recent results ( [14,15,16] of CCC theory, the most extensively applied theory to the problem to date. For the status of the CCC and some other methods the review article by Briggs and Schimdt [17] may be seen.…”

Single and triple differential cross sections for double photoionization ofH−

“…Since the optical absorbtion is described by a sum of one-body dipole operators, any theoretical approach that treats the electrons in an independent particle model will produce inaccurate results for the amplitudes connecting the initial and final states. Such considerations have been previously addressed using different theoretical approaches for both atomic [12][13][14][15][16][17][18][19][20][21][22][23][24][25] and molecular [26][27][28][29] two-electron targets, with varying degrees of electron correlation being included in the initial and/or final states.…”

“…Since the pioneering theoretical work of the 1960s [30][31][32] to describe the correct asymptotic form of the wavefunction and the accompanying double ejection amplitude, numerous efforts have been applied to the more general three-body Coulomb breakup problem, including the use of anzatz wavefunctions [12][13][14], convergent close-coupling (CCC) methods [15][16][17][18], adapted R-matrix techniques [19,20], time dependent close coupling (TDCC) methods [21][22][23], complex basis functions [24], and finally the method of exterior complex scaling (ECS) [25,33,34]. In addition to ensuring that the calculated wavefunctions maintain the proper boundary conditions for three-body breakup, each method requires a proper means to extract the physically relevant amplitude associated with the two-electron outgoing wave to produce cross sections that can be compared with experiment.…”