Electron removal from atomic hydrogen by collisions with fully stripped oxygen ions

Cross sections for charge transfer and impact ionization in ${\mathrm{O}}^{8+}$ + H collisions have been calculated in the range of collision velocities (0.1-10) × ${10}^8$ cm/sec. At the lower velocities, up to 1.2 × ${10}^8$ cm/sec, charge-transfer cross sections were determined by means of the perturbed-stationary-state method in the impact-parameter approximation with a selective basis set of adiabatic one-electron two-center orbitals. The charge-transfer cross section increases monotonically in this region, attaining a value of 8 × ${10}^{-15\mathrm{}}$ ${\mathrm{cm}}^2$ at 1.2 × ${10}^8$ cm/sec. Rotational coupling was found to be an important mechanism which contributes significantly to the large cross sections in the molecular regime. Thus the present results are at least a factor of 2 larger than previous Landau-Zener calculations. Above 2.2 × ${10}^8$ cm/sec, a classical-trajectory Monte Carlo approach was used to compute both charge-transfer and ionization cross sections. At velocities above 5 × ${10}^8$ cm/sec, ionization becomes the dominant electron-removal process.