Experimental absolute cross section for photoionization of Xe$^{7+}$

Collision processes with highly charged xenon ions are of interest for UV-radiation generation in plasma discharges, for fusion research and for space craft propulsion. Here we report results for the photoionization of Xe$^{7+}$ ions\footnote{S. Schippers et al., J. Phys.: Conf. Ser. (in print)} which were measured at the photon-ion end station of ALS beamline 10.0.1. As compared with the only previous experimental study\footnote{J. M. Bizau et al., Phys. Rev. Lett. 84, 435 (2000)} of this reaction, the present cross sections were obtained at higher energy resolution (50--80~meV vs.\ 200--500 meV) and on an absolute cross section scale. In the experimental photon energy range of 95--145~eV the cross section is dominated by resonances associated with $4d\to 5f$ excitation and subsequent autoionization. The most prominent feature in the measured spectrum is the $4d^9\,5s\,5f\,{^2\!P}$ resonance at $121.14\pm0.02$~eV which reaches a peak cross section of 1.2 Gb at 50~meV photon energy spread. The experimental resonance strength of 160~Mb~eV (corresponding to an absorption oscillator strength of 1.46) is in fair agreement with the theoretical result$^2$.