Electron capture inC6++He andO8++He collisions at intermediate energies in the atomic-orbital-expansion method

A multistate two-center atomic-orbital-expansion method is applied to study the subshell capture cross sections from helium atoms in collisions with bare ${\mathrm{C}}^{6+}$ and ${\mathrm{O}}^{8+}$ ions. The energy dependence of subshell capture cross sections, i.e., the n, nl, and nlm distribution, is examined. In view of the lack of detailed subshell cross section measurements, we compare our calculations with experimental total capture cross sections and with polarization fraction for the 2p-1s transition in ${\mathrm{O}}^{8+}$-He collisions. For the latter process, the cascade effect must be included in the theoretical analysis. We show that our results are in good agreement with existing experimental data.