Excitation ofHe+by electron impact

Abstract

A five-state close-coupling approximation in which $1s$, $2s$, and $2p$ eigenstates and $\overline{3s}$ and $\overline{3p}$ pseudostates of ${\mathrm{He}}^{+}$ are included in the expansion, is used to calculate $1s\to 2s$ and $1s\to 2p$ excitation of ${\mathrm{He}}^{+}$ by electron impact in the intermediate energy range up to about three times ionization threshold energy. Pseudostates are chosen to maximize their overlap with bound states and low-lying continuum states of the same symmetry. Present results for $1s\to 2s$ excitation provide a link between accurate low- and high-energy results and agree with experiment above 70 eV.