A theoretical and experimental study of the photoionization of Al$^+$.

High resolution photoionization cross section measurements have been made at ALS, corresponding to the $2p$ excitation (photon energy $>$80eV) of the Al$^+$ ground state $2p^63s$. These, with absolute measurements from ASTRID [1] for energies 20-160eV, are compared to data from R-matrix calculations. In the near threshold region ($<$25eV), theory detects two $3pns\,^3P^{\rm o} $ resonance series, a $3pns\,^1P^{\rm o}$ and a $3pnd\,^1P^{\rm o}$ series. The experiment [1] detects a single $3pns$ series and we find excellent agreement with the theoretical positions. Above the $2p$ ionization threshold, the ALS data shows much more detail and by comparing with oscillator strengths and resonance positions from the calculation we identify much of the resonant structure. [1] West et al, 2001, PRA 63, 052719