Three-body Coulomb description of pionic helium

The three-body Schrodinger equation of the system composed of an alpha particle He2+, a negatively charged pion pi(-), and an electron interacting through Coulomb forces is solved in perimetric coordinates with the Lagrangemesh method. The ground state, quasibound states, and resonances are obtained for total orbital momenta L = 0 - 20. Mean distances between the particles allow for identifying the structure of these states. The widths of resonances broader than 10(-5) atomic units are derived with the complex scaling method. A transition from atomic to molecular structure occurs between L = 10 and L = 13. Excited levels obtained for L = 0 - 5 display hydrogenlike properties for both the alpha-pion system and the electron excitations. Excited levels with L >= 14 correspond to a vibrational excitation of the relative motion of the heavy particles. The validity of the Born-Oppenheimer approximation is found to be fair over the whole range of total orbital momenta.