Measurements of absolute photoionisation cross sections of Ga+and Zn+ions

Measurements are reported of absolute photoionisation cross sections of Zn + and Ga + ions by VUV radiation. Both cross sections were dominated by autoionisation resonances. For Ga + the largest resonances had cross sections of 3*10 -16 cm 2 and were centred about 21.88 eV. This is similar to the energy of 21.9 eV calculated by Pindzola et al (1982) for 3d 10 4s 2 to 3d 9 4s 2 4p 3 P 1 . Comparisons were also made with the spectrum of atomic zinc measured by Marr and Austin (1969). For Zn + some photoionisation resonances could be related to autoionising transitions in the electron impact ionisation cross sections reported by Rogers et al (1982) but the strongest electron-impact-induced transition does not appear in the photoionisation spectrum.