Single differential cross-sections for transfer-loss (TL) leading to the production of O5+(1s2s³S)nl4L states were computed for 0.2-1.2 MeV/u collisions of O5+(1s²2s) ions with He and H2 targets. At these collision energies, 1s loss is significant and electron transfer to n = 3-4 levels is dominant. Furthermore, due to spin conservation, quartet states can only be populated by TL. Within the independent particle model (IPM), the probability of 1s electron loss from O5+(1s²2s) projectiles was calculated using the semi-classical approach, while the probability for electron transfer to the O5+(1s2s³S)nl4L states (n > 2) was computed using the continuum distorted wave (CDW) approximation. The majority of states with n > 2 can be assumed to have sufficient time to eventually decay with an almost 100% probability to the long-living metastable 1s2s2(4)P level via a much faster sequence of electric dipole transitions, thus establishing an upper limit to such cascade contributions. The inclusion of this cascade feeding is found to lead to a strong enhancement in the production of the 1s2s2p4P states, particularly for collisions with the H2 target, thus reducing dramatically the existing two-order of magnitude discrepancy between older TL calculations (for n = 2 only) and existing zero-degree Auger projectile electron spectroscopy measurements.
Metastable states; Cascade feeding; Ion-atom collisions; Electron capture
