The $1s\to 2s$ and $1s\to 2p$ excitations of the hydrogenic ions ${\mathrm{C}}^{5+}$ and ${\mathrm{O}}^{7+}$ are studied using a pseudostate expansion. A small ($3-s$, $3-p$) basis is used above the $n=3\mathrm{}$ threshold while in the resonance region between the $n=2\mathrm{}$ and $n=3\mathrm{}$ thresholds a larger ($6-s$, $5-p$, $2-d$, and $1-f$) set is employed. The coupled integrodifferential equations are solved by a variational approach. High-energy and high-$L$ results are found using the Coulomb-Born approximation with exchange. Positions and widths of resonances are given. An analytic fit to the calculated $K$ matrices is used to determine cross sections in the resonance region. Excitation rates are computed.

• Received 22 June 1981

DOI:https://doi.org/10.1103/PhysRevA.24.2372