Differential Cross Sections for H 2s–3s Excitation by Electron and Positron Impact

Abstract

Electron and positron impact di †erential cross sections for excitation of the 3s state of a hydrogen atom from its metastable 2s state are calculated in a distorted wave approximation at 10 and 50 eV. The e †ects of both adiabatic and non-adiabatic distortion of the atomic charge cloud by the incoming electron or positron are included in the initial and Ðnal state wavefunctions. Contrary to an earlier prediction, no dramatic di †erences between the electron and positron results are found.

2s–3s excitation for positron–metastable hydrogen collisions

“…Full optical potential (continuum optical potential plus positronium formation optical potential) (solid), continuum optical potential only (dotted) and pure close coupling (dashed) results are presented in (a). A comparison between the present CCOB results (solid), the results of Jha et al [8] (dashed), Deb et al [9] (dash dotted) and Kulhar [11] (dotted) is shown in (b). can be seen in figures 2(a) and 3(a), the effects of optical potentials become weak as the incident energy increases and they only cause a slight difference in the magnitude of cross sections.…”

“…The results of Jha et al [8] showed sharp dips in the curves of the differential cross section for both energies, while Kulhar [11] obtained shallow minima at different scattering angles. There was no dip in the results of Deb et al [9] and Ghoshal and Mandal [10]. Polarization potentials were taken into account in the calculation of the incoming wavefunction in the work of Deb et al [9].…”

“…There was no dip in the results of Deb et al [9] and Ghoshal and Mandal [10]. Polarization potentials were taken into account in the calculation of the incoming wavefunction in the work of Deb et al [9]. Kulhar [11] included the polarization of the target by the second-order term in their matrix element, while only the static potential of the initial metastable state was taken as the distorting potential in the work of Jha et al [8].…”

“…Excitation from the ground state hydrogen to higher states by positron impact has been extensively studied by various approaches [1][2][3][4][5][6][7], whereas only limited theoretical methods have focused on the investigation of the interaction of positron with the excited state hydrogen. Earlier distorted-wave calculations based on a two-potential approach have been performed by Jha et al [8] and Deb et al [9]. They chose different distortion potentials to calculate the differential cross sections for the 2s-3s excitation at two impact energies, 10 and 50 eV.…”

“…They chose different distortion potentials to calculate the differential cross sections for the 2s-3s excitation at two impact energies, 10 and 50 eV. Jha et al [8] took the static potential of the initial metastable state as the distortion potential, while the effects of both adiabatic and non-adiabatic distortions of the atomic charge cloud by the incoming positron were included in the initial and final state wavefunctions in the calculations of Deb et al [9]. Recently, Ghoshal and Mandal [10] calculated the differential and integrated cross sections for Rydberg transitions in the energy range 20-300 eV within the framework of the distorted-wave theory by approximating the distortion potential in a particular channel as the average of perturbation of that particular channel over the bound states in the momentum space.…”