Features of the differential cross section in the 2s-3s excitation of the hydrogen atom by electron and positron impact

Abstract

Differential cross sections for the 2s-3s excitation of hydrogen atoms by electron and positron impact are reported at two incident energies, 10 eV and 50 eV, using a distorted wave method based on the two potential model. Dramatic differences between the electron and positron results are noticed at both energies.

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.…”

“…From figures 1(b) and 3(b) we see great disagreement among these curves obtained with different theoretical models at intermediate and large scattering angular regions. 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].…”

“…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.…”

Methods and progress in studying inelastic interactions between positrons and atoms

“…Using their high resolution trapped positron source, they studied vibrational and electronic excitation of H 2 , N 2 , CH 4 and Ar and found comparable cross sections for positron and electron impact in the threshold region. Theories, on the other hand, predict differences in the total and differential cross sections (Walters 1988, Jha 1994, Lino et al 1994. Indirect information about projectile excitation in Ps-atom collisions was obtained by Szluińska et al (2002b) but, overall this area will probably stay mostly unexplored until more intensive positron beams become commonly available.…”