Low-energy electron-impact ionization of the helium atom using the multiconfiguration Hartree-Fock method

Abstract

We have extended the multiconfiguration Hartree-Fock method for electron-impact ionization of atoms to investigate the effects of polarization and electron correlation of the target in the initial state. As a test case, the method is applied to calculate triple differential cross sections for electron-impact ionization of He atom at an excess energy of 2 eV for the coplanar θ 12 = π geometry for equal and unequal energies of two final-state outgoing electrons. To determine the effects of electron correlation between the two outgoing electrons in the final state, the variationally determined screening potential approximation is used. It is found that target correlation in the initial state has smaller effect on the triple differential cross section but the polarization of the target by the incident electron has considerable effect on the triple differential cross section at low incident energy. The results are compared with absolute measurement and other available theoretical results.

Small device-to-device variation of 6,13-bis(triisopropylsilylethynyl)pentacene field-effect transistor arrays fabricated by a flow-coating method

“…As mentioned earlier, we previously reported the results of our investigation on TDCS for electron impact ionization of H and He atoms using the HF and the SP approximations for 12 θ π = symmetry. The results were very encouraging.…”

“…The numerical procedure as adopted in the MCHF method [13,12] for both bound and continuum electrons is used to calculate wave function for each of the final state continuum electrons in the SP approximation. In the SP approximation, since the effective charges are angle dependent, the wave functions are calculated for each relative angle for both equal and unequal energies and for several angular momentum l = 0 to l 6 = and for the partial wave L 0 6 = − and S 0 1 = − .…”

“…The results were in very good agreement with relative experimental measurements and other accurate calculations. Later we also performed similar calculations for the helium target [12,13] using the MCHF method, at low incident electron energies to determine the effects of electron correlation and polarization of the target completely ab initio. We found that polarization of the target by the incoming electron has considerable effects in the TDCS for the electron impact ionization of the He atom.…”

“…In both equal and unequal sharing of excess energy, the results with polarization in the initial state and SP approximation in the final state provide excellent agreement with experiment at all angles considered by the experiment. These calculations are performed for the simple case 12 θ π = symmetry. In this paper we have investigated the application of SP approximation toward the study of TDCS for other kinematics and collision geometry which will probe the collision dynamics for He.…”

Extension of the multiconfiguration Hartree-Fock method to allow double photoionization of atoms

“…In addition, the existing theoretical calculations on the heavier atom could not produce very good agreement with experimental results. These discrepancies between the experimental measurement and theoretical results inspired us to extend the MCHF method [18][19][20][21] to study the DPI of atoms. Moreover, although few ab initio methods are successful in explaining the experimental measurements, we believe that it is always good to develop a theoretical model which can explain the angular distribution of two photoelectrons very efficiently.…”