The antiprotonic helium atom

The Born-Oppenheimer approximation is used to discuss the high rotational and vibrational state of the (He p⁻)e⁻ system in the electronic 1sσ and 2pσ states. Very high angular momentum states, in which the antiproton is well outside the electron orbit, have a Rydberg-like character. states in which the antiproton is within the 1sσ electron orbit have enhanced radiative lifetimes due to the polarization of the 1sσ state by the antiproton. This effect may account for the long-lived component observed in antiproton destruction in He. Preliminary results on the effect of coupling to the 2pσ well, in which the polarization effects enhance the decay rate, are also presented. Some consequences for the suggestion that metastable antiprotonic He atoms may be used to promote antihydrogen formation are discussed.