Unwanted effects can be generated in photoelectron spectra by minority emissions which commonly appear in rare gas sources of resonance line uv radiation. Such emissions probably account for certain observed states of both NO+ and Hg+. Tables of spectra from several sources are given, and useful spectral cleanup is demonstrated with zeolite gas trapping.
R. B. Cairns, H. Harrison, and R. I. Schoen, "Photoelectron Spectroscopy With Undispersed Ultraviolet Radiation," Appl. Opt. 9, 605-608 (1970)