B-splineR-matrix-with-pseudostates approach for excitation and ionization of atomic oxygen by electron collisions

Abstract

Electron scattering with atomic oxygen has been studied using the $B$-spline $R$-matrix-with-pseudostates method. Cross sections for elastic scattering, excitation, emission, and ionization processes are presented. The excitation cross sections have been calculated for transitions between the $2{s}^{2}2{p}^{4}$ and $2{s}^{2}2{p}^{3}3l$ states of oxygen in the energy range from threshold to 200 eV. The present work differs from numerous previous studies due to the inclusion of a large number of pseudostates in the calculation. We included a total of 1116 spectroscopic bound, core-excited autoionizing, and target continuum states in the close-coupling expansion. The atomic oxygen structure model has been described by combining the multiconfiguration Hartree-Fock and the $B$-spline box-based multichannel methods. The inclusion of a large number of pseudostates representing the target continuum has a major impact, especially on the theoretical prediction of the excitation cross sections for many transitions at intermediate energies. A large reduction in excitation and emission cross sections has been noted due to the inclusion of coupling to the ionization continuum. The calculated cross sections are now in better agreement with available experimental results. The ionization cross sections for the ground $2{s}^{2}\phantom{\rule{0.16em}{0ex}}2{p}^{4}{\phantom{\rule{0.16em}{0ex}}}^{3}P$ and metastable $2{s}^{2}2{p}^{4}{\phantom{\rule{0.16em}{0ex}}}^{1}D$ and $^{1}S$ states are also presented. The electron-impact-induced emission cross sections for the $(2{s}^{2}2{p}^{3}3s){\phantom{\rule{0.16em}{0ex}}}^{3}{S}^{o}--(2{s}^{2}2{p}^{4}){\phantom{\rule{0.16em}{0ex}}}^{3}P$ (130.4 nm), $(2{s}^{2}2{p}^{3}3d){\phantom{\rule{0.16em}{0ex}}}^{3}{D}^{o}--(2{s}^{2}2{p}^{4}){\phantom{\rule{0.16em}{0ex}}}^{3}P$ (102.7 nm), $(2{s}^{2}2{p}^{3}3{s}^{\ensuremath{'}}){\phantom{\rule{0.16em}{0ex}}}^{3}{D}^{o}--(2{s}^{2}2{p}^{4}){\phantom{\rule{0.16em}{0ex}}}^{3}P$ (98.9 nm), and $(2{s}^{2}2{p}^{3}3{s}^{\ensuremath{'}\ensuremath{'}}){\phantom{\rule{0.16em}{0ex}}}^{3}{D}^{o}--(2{s}^{2}2{p}^{4}){\phantom{\rule{0.16em}{0ex}}}^{3}P$ (87.8 nm) transitions have been calculated and compared with the available experimental results.