We have performed the first excitation of high-n states of positronium using resonant, two-photon excitation applied to the n=1 to 2 and 2 to n transitions. Absolute values for the line positions were quantitatively determined for n=14 and 15 and compared well with calculated predictions. The prediction of the ${\mathit{n}}^{\mathrm{-}3}$ scaling of the relative transition rates was observed for n=12 to 19.

• Received 30 October 1989

DOI:https://doi.org/10.1103/PhysRevLett.64.2366