The capture of slow antiprotons in noble gases

The capture of slow antiprotons (energies less than 1.0 au, i.e. roughly 27 eV) by the rare gas atoms helium, neon and argon is considered. Appropriat e to this low velocity, the capture cross sections are calculated using the adiabatic 'hidden-crossing' theory in which the collision complex is viewe d as a transient diatomic molecule with the positively-charged atomic ion a nd antiproton as nuclei. In addition to the total capture cross section, es timates of the percentage population of long-lived 'circular' states is giv en. Our calculations suggest that a few per cent of captured antiprotons oc cupy these states in helium but in the case of argon or neon the probabilit y of primary capture into such long-lived states is negligible. These resul ts are at variance with previous calculations of antiproton capture cross s ections.