Regular Article

Antiproton-impact ionization of hydrogen atom with Yukawa interaction

¹ Department of Physics, Sts Cyril and Methodius University, P.O. Box 162, 1000 Skopje, Macedonia
² Institute of Physics, University of Belgrade, P.O. Box 57, 11001 Belgrade, Serbia
³ Macedonian Academy of Sciences and Arts, P.O. Box 428, 1000 Skopje, Macedonia

^a e-mail: dragan.jakimovski@gmail.com

Received: 21 August 2017
Received in final form: 22 October 2017
Published online: 18 January 2018

Abstract

The process of ionization of hydrogen atom by antiproton impact is studied when the interparticle interactions in the system are described by screened interactions of Yukawa type. The collision dynamics is described by the semiclassical atomic-orbital close-coupling method in which the bound atomic states and positive energy continuum pseudostates are determined by diagonalization of target Hamiltonian in a sufficiently large even-tempered basis to ensure convergence of the results at each value of the screening length λ of the interaction. With decreasing the screening length, the bound states in the Yukawa potential become unbound, thus increasing the number of continuum pseudostates. At low collision energies, this leads to the increase of the ionization cross section. It is observed that the energies of pseudostates, generated by the exit of nl bound states in the continuum, at certain critical values λ_nl^c exhibit series of avoided crossings when λ is varied. The avoided crossings appear between the (n + k) l and (n + k + 1) l (n = 1, 2, 3, … ; k = 0, 1, 2, …) states at screening lengths close to the critical screening length λ_nl^c. The avoided crossings become increasingly less pronounced with increasing n, k and l. The matrix elements for the (n + k) l - (n + k + 1) l transitions at the avoided crossings λ_x,(n+k)l^(n+k+1)l exhibit maxima and are reflected in the structure of the cross sections for population of the lower nl pseudostates. These structures are, however, smeared out in the total ionization cross section.