Along its lowest rotational band, the antiprotonic helium atom undergoes several changes of structure. It evolves from an hydrogenlike atom with broader and broader resonant states, to a quasistable molecularlike structure with narrow resonances, and then to a quasistable Rydberg pseudoatom. The antiprotonic helium atom is studied with high accuracy as a nonrelativistic three-body Coulomb system in the framework of the Lagrange-mesh method. Its metastable states are first determined from $L=0$ to $L=80$ by searching conditions of calculation for which energies are stationary. Mean values of distances between the particles are then easily deduced. They show the evolution of the structure of the system. Broad resonances are also analyzed with the complex scaling method. Physical interpretations are provided.

• Received 14 November 2018

DOI:https://doi.org/10.1103/PhysRevA.99.022508