State-selective electron capture by O³⁺ ions from atomic and molecular targets

State-selective electron-capture processes in low-energy collisions of O³⁺ recoil ions with He, Ar, D₂, O₂, H₂O, and CO₂ at impact energies between 0.3 and 1.2 keV and scattering angles between 0° and 6° have been studied using a differential energy-gain spectrometer, capable of measuring simultaneously the energy-gain and the scattering angle of projectile products in ion-atom and -molecule collisions. The energy-gain spectra show that the dominant reaction channels are due to capture into excited states of the projectile product O²⁺. In this work, no clear evidence of the processes involving long-lived metastable state O³⁺ (2s2p^2 4P) was observed. The energy-gain spectra are interpreted qualitatively in terms of the reaction windows, which are calculated using the single-crossing Landau-Zener model and the extended version of the classical over-the-barrier model. The energy dependence of cross sections for electron capture are also measured and found to be nearly constant with changing collision energy. The data are also compared with available measurements and calculations and theoretical results based on the multichannel Landau-Zener model.