Inner-shell photoionization of stored positive ions using synchrotron radiation

We have measured the distribution of photoion charge states resulting from vacancy cascades and electron shakeoff following K-shell photoionization of ${\mathrm{Ar}}^{2+}$ ions. The ${\mathrm{Ar}}^{2+}$ ions were produced by electron-impact ionization of Ar, stored in a Penning ion trap, and then photoionized using broadband synchrotron radiation. Time-reversed integration of coupled differential equations was used to account for contributions from electron capture with residual gas. The results are in reasonable agreement with a simple theoretical prediction.