Excitation of hydrogenlike ions by electron impact

A method is formulated for the straightforward evaluation of the Coulomb-Born and Coulomb-Born-Oppenheimer (CBO) cross sections for $1s$-$2s$ excitation of hydrogenlike ions by electron impact, without employing partial-wave analysis. The simplicity of the method makes it very economical for the calculation of electron-ion scattering cross sections at any energy. Some results for the $1s$-$2s$ excitation cross sections for hydrogenlike ions with Z=2, 3, 6, 10, and 50 are presented. The high-energy CBO results for the $1s$-$2s$ excitation of He⁺ agree well with recent experimental findings.