Measurement of the absolute photoionization cross section of C+ near threshold

The absolute photoionization cross section of the ground-state C+ ion has been measured from the ionization threshold at 24 eV to 31 eV using a merged ion-photon beam setup with synchrotron radiation from an undulator. The experimental results have been compared with nonrelativistic theoretical data from the Iron Project and the agreement is generally good in the near-threshold region, but differences in the magnitude of the continuum cross section of 15%-35% at higher energies and several deviations in the resonance structure are observed. The present measurements are a part of an experimental program to test the extensive theoretical photoionization cross section calculations performed within the framework of the Opacity Project and the Iron Project.