Energy-gain spectroscopy studies of Oq+ (q = 2-5) collisions with He atoms

Energy-gain measurements have been performed on single-electron capture reactions with low-energy Oq+, q = 2-5, colliding with He. Total and (for the main capture channels) partial absolute cross sections have been determined in O2+-He for projectile energies 100-300 eV, in O3+-He for projectile energies 250-1500 eV, in O4+-He for projectile energies 200-1000 eV and in O5+-He for 500 eV projectile impact energy. For O2+ our results agree quite well with earlier experimental total cross section measurements and to a certain extent with theoretical partial cross section calculations. For Oq+, q = 3-5, no data exist in the literature for this energy region. Our total cross section for single electron capture by O3+ from He is a factor of 3 larger than available fusion-oriented estimates. For O4+-He the total cross section is small for the ground-state 1S projectile, and a small fraction of the metastable 3P0 component influences the energy-gain spectrum through its larger cross section. For O5+-He the total cross section is large. An analysis has been made of the angular scattering present in the collision systems and theoretical energy gain spectra have been used in assignment of reaction channels, in handling the problem of metastables and to some extent also in interpreting partial cross sections for close-lying channels. (orig.)