Extreme-ultraviolet spectroscopy of highly charged xenon ions created using an electron-beam ion trap

Extreme-ultraviolet spectra of xenon ions have been recorded in the 4.5 to 20 nm wavelength region using an electron beam ion trap and a flat field spectrometer. The electron beam energy was varied from 180 eV to 8 keV and radiation from charge states Xe⁶⁺ to Xe⁴³⁺ was observed. Our measured wavelengths were compared to atomic structure calculations using the Cowan suite of codes. We have measured seventeen previously unreported features corresponding to transitions in Xe³⁵⁺ through to Xe⁴¹⁺ with estimated wavelength uncertainties of ±0.003 nm. It was found that for the case of continuous injection of neutral xenon gas a wide range of charge states were always present in the trap but this charge state distribution was greatly narrowed, towards higher charge states, if a sufficiently low gas injection pressure was employed. The energy dependence of spectral lines arising from Xe⁴²⁺ and Xe⁴³⁺ revealed enhancement of the total ionization cross sections, due to excitation-autoionization of n=2 electrons to n=3 levels, in the Xe⁴¹⁺ and Xe⁴²⁺ charge states.