Scattering of positronium from singly ionized helium and appearing resonances
The coupled-channel model [Phys. Rev. A {\bf 59}, 363 (1999)] that yields converged low-energy phase shifts, and exact binding and resonance features in Ps-H [Phys. Rev. A {\bf 59}, 2058 (1999)] is applied to study Ps-He$^+$ scattering. Similar to PsH, resonances appear in the S-, P-, D-, etc partial waves in the Ps-He$^+$ system but in both the singlet and triplet scattering channels. The latter signifies possible Rydberg states of $e^+$ around singlet and triplet helium. The S-wave singlet resonance at 2.79 eV agrees to that predicted earlier in $e^+$-He entrance channel (energy difference 16.64 eV) at 19.27 eV [Chem. Phys. Lett. {\bf 262}, 460 (1996)].