A theoretical and experimental study of the photoionization of AlII

High-resolution photoionization cross section measurements have been made at the ALS, corresponding to the 2p excitation (photon energy > 80 eV) of the AlII ground state 2p⁶3s². Previous absolute measurements from ASTRID are available for energies 20–160 eV. R-matrix calculations have been carried out and comparison is made with the measured data. In the near threshold region (<25 eV), theory predicts two 3pns ³P^o resonance series, a 3pns ¹P^o and a 3pnd ¹P^o series. The experiment detects a single 3pns series and we find excellent agreement with the theoretical positions. Above the 2p ionization threshold, the ALS data show much more detail and by comparing with oscillator strengths and resonance positions with the calculation we identify much of the resonant structure.