Total photoionization cross sections of atomic oxygen from threshold to 44.3 Å

The relative photoionization cross section of atomic oxygen for the production of singly charged ions has been remeasured in more detail and extended to cover the wavelength range 44.3–910.5 Å by use of synchrotron radiation. In addition, the contribution of multiple ionization to the cross sections has been measured, allowing total photoionization cross sections to be obtained below 250 Å. The results have been made absolute by normalization to our previously measured data. The use of synchrotron radiation has enabled measurements of the continuum cross section to be made between the numerous autoionizing resonances that occur near the ionization thresholds. This in turn has allowed a more critical comparison of the various theoretical estimates of the cross section to be made. The series of autoionizing resonances leading to the ${}_{}{}^4{}_{}{}^{}\mathrm{P}$ state of the oxygen ion have been observed for the first time in an ionization-type experiment, and their positions have been compared with both theory and previous photographic recordings.