L. U. Ancarani

Double ionization of two-electron systems

We address various issues related to the double ionization by electron impact of two-electron systems. The emphasis will be put on the theoretical description of high incident energy (e,3e) processes, for which the first Born approximation should be suitable. In the case of helium, absolute experimental data for fivefold differential cross sections are available in coplanar geometry. We will review and discuss the divergencies existing between the results obtained with different theoretical models, and those appearing when compared to the experiments in particular with respect to the absolute scale. We will then discuss some results obtained in a recently proposed out of plane geometry.

A simple parameter-free wavefunction for the ground state of three-body systems

We propose a simple wavefunction for the ground state of general atomic three-body systems in which two light particles are negatively charged and the third (heavy) is positively charged. By construction this wavefunction (i) has the same analytical form for all systems; (ii) is parameter-free; (iii) is nodeless; (iv) satisfies all two-particle cusp conditions; and (v) yields reasonable ground-state energies for several three-body systems, including the prediction of a bound state for H−, D−, T− and Mu−. For illustration, results are given for several three-body systems, and in particular for variants of helium-like ions. We provide analytical formulae, as well as simple polynomial fits for certain subcases, which allow one to have a rapid estimate of the ground-state energy and to study the stability for quite general cases.

Theoretical Investigation of the p + He H + He + and p + He H + He ++ + e Reactions at Very Small Scattering Angles of Hydrogen

A hypothesis is considered that the reactions p + He → H + He+ and p + He → H + He++ + e at very small scattering angles of hydrogen can be used for the angular spectroscopy of electron correlations in a target. It is shown that this hypothesis is inconsistent.

Comment on 'New geometry for the quasi-binary incident electron–centre of mass collision in the (e, 3e) process on He'

In a recent publication, Choubisa and Sud (2008 Journal of Physics B: At. Mol. Opt. Phys. 41 035202) investigated (e, 3e) processes and compared their calculations with available absolute experimental data. According to the authors, the results (within the first and second Born approximation) were obtained using the 3C model for the final double-continuum state and two different helium ground initial states. As all these model wavefunctions are not properly defined, the paper introduces confusing ideas that need to be clarified to the community. In particular, we show here that they do not use the 3C model, but an approximate version which largely underestimates the cross sections. Furthermore, the authors propose an interesting new geometry, but again present peculiar results that must be clarified.

On the numerical treatment of Coulomb forces in scattering problems

We investigate the limiting procedures to obtain Coulomb interactions from short-range potentials. The application of standard techniques used for the two-body case (exponential and sharp cutoff) to the three-body break-up problem is illustrated numerically by considering the Temkin-Poet (TP) model of e-H processes.

Explicitly correlated Sturmian functions for structure and collision three-body problems

We introduce explicitly correlated Sturmian functions with appropriate boundary conditions to deal with both bound and scattering states of three-body systems.

Ground state for two-electron atoms in exponential-cosine-screened Coulomb potentials

We extend the Angular Correlated Configuration Interaction method to two-electron atoms placed in a plasma environment.

Hyperspherical versus spherical treatment of asymptotic conditions for three-body scattering problems

We consider two different Sturmian Function (SF) expansions to describe three-body break-up wave functions having outgoing flux behavior: one in hyper-spherical coordinates (ρ and α) and one in spherical coordinates (r1 and r2). We compare the convergence rates of the two treatment, and relate the analysis to geometry aspects of the problem.

Use of uncorrelated Sturmian basis functions for three-body systems of finite masses

The Configuration Interaction method with uncorrelated Sturmian basis functions is applied to describe a variety of atomic and molecular three-body systems.

An analytically solvable model to test the hyperspherical Sturmian approach for break up processes

An analytically solvable model for three particles break up processes is presented. The scattering process is represented by a non-homogeneous Schrodinger equation where the driven term is given by a Yukawa-like interaction multiplied by the product of a continuum wave function and a bound state in the particles coordinates. A closed form solution is derived in hyperspherical coordinates (ρ,α). This leads to an analytic expression for the transition amplitude associated to the scattering process. This model is used to test calculations performed within the frame of an hyperspherical Sturmian approach.