High-angular-momentum resonances in positron scattering by aHe+ion

The method of complex-coordinate rotation is applied to investigate resonances in positron scattering by helium ions. Here we present results for high-angular-momentum states $(L=2--6).$ Together with the earlier values for the $L=0$ and 1 states, these stabilized complex eigenvalues exhibit a regular pattern. We also calculate some narrow S-wave resonances below the excited positronium $(N=2)$ threshold. Our converged results for the first S state lying above the ${\mathrm{He}}^{+}$ $(n=5)$ threshold differ substantially from the calculation by Igarashi and Shimamura [Phys. Rev. A 56, 4733 (1997)].