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