Triple differential cross section calculation for the helium autoionization by electron impact

Abstract

The triple differential cross section and autoionization a and b parameters, as functions of ejected electron angle, have been calculated for the helium (2s2)1S, (2s2p)1P and (2p2)1D resonances in the coplanar asymmetric (e,2e) reaction for the incoming electron energy/scattering angle kinematical conditions of 400 eV/16 degrees , 200 eV/13 degrees and 100 eV/13 degrees . Configuration interaction expansions for the resonances and helium ground state which employed hydrogenic and multiconfiguration Hartree-Fock orbitals, respectively, were used in the present study. The distorted wave Born approximation, with exchange, was employed for the (e,2e) cross section calculation with the distorted waves being calculated in the Hartree-Fock potential of the helium neutral atom or the positive ion. Calculated parameters agree well with experimental 400 eV/16 degrees data whereas only a qualitative resemblance exists for 200 eV/13 degrees and 100 eV/13 degrees kinematics.

Nondipolar photoionization of atoms

“…This value differs significantly from the theoretical predictions q 2¨ 1 [17,18]. This quantity is not accessible in scattering experiments.…”

Theoretical triple differential cross section of the helium atom ionization with excitation to then=2 ion state

“…, which recovers 95.4% of the correlational energy. Increasing the number of terms in the MCHF expansion s1ightly improves the correlational energy [14] but does not affect significantly excitation and ionization amplitudes. The six-term expansion {1) is a reasonable compromise between the required accuracy and computational ef5ciency.…”

“…This is a highly correlated and rapidly convergent wave function recovering a significant part of the correlational energy, even with a small number of configurations. It has been used successfully for the description of the helium atom resonance ionization [14] and ionization with excitation in the limit of large energy transfer [15]. To calculate the final-state wave function of the system, ion plus the "slow" ejected electron, we employ a coupled-channel (CC) formalism.…”

Nondipole parameters of TDCS for electron impact ionization and drag current

“…Integration of the DDCS in Eq. (14) over Ω gives 4πδ L0 , which eliminates all the terms in this equation except the term with L = 0. The double differential cross-section for the scattering of the fast charged particle, differential in energy loss and scattering angle, has the form…”

“…Therefore, among the numerous studies of the TDCS (both experimental and theoretical [11][12][13][14][15][16][17][18][19]), an important place is occupied by investigations focusing specifically on studying of the TDCS in the optical limit (see, for example [20] and references therein), when the cross-section for a small amount of transferred momentum q can be represented as a power series in momentum. In the limit → 0 the TDCS is well described by the dipole approximation [21][22][23].…”