Absolute photoionization cross section of K+ ions from the 3p to the 3s threshold

The absolute photoionization cross section of ground state K+ ions has been measured from the 3p threshold to above the 3s threshold (31-49 eV) by VUV radiation using a merged ion-photon beam set-up. The cross section, which reaches a maximum value of 32 Mb +/- 10% at 31.8 eV and then decreases with energy, is in overall good agreement with absolute measurements by Peart a nd Lyon, but the present investigation also reveals the 3s3p(6)np P-2 (n = 4-6) resonances and eliminates a previously unassigned structure at 35.5 eV . The energies, widths and shape parameters of the autoionizing P-2 resonan ces are determined and compared with recent data from dual-laser plasma mea surements and with theoretical predictions. The present experimental set-up will allow absolute photoionization cross sections less than or equal to 0 .1 Mb to be measured, making it possible to measure the absolute photoioniz ation cross sections of ions of astrophysical importance.