  Molecular oxygen, nitrogen, and ozone have been detected in the Solar System.
They are also expected to be present in ice-grain mantles within star-forming
regions. Laboratory experiments that simulate energetic processing (ions,
photons, and electrons) of ices are essential for interpreting and directing
future astronomical observations. We provide VUV photoabsorption spectroscopic
data of energetically processed nitrogen- and oxygen-rich ices that will help
to identify absorption bands and/or spectral slopes observed on icy objects in
the Solar System and on ice-grain mantles of the interstellar medium. We
present VUV photoabsorption spectra of frozen O2 and N2, a 1:1 mixture of both,
and a new systematic set of pure and mixed nitrogen oxide ices. Spectra were
obtained at 22 K before and after 1 keV electron bombardment of the ice sample.
Ices were then annealed to higher temperatures to study their thermal
evolution. In addition, Fourier-transform infrared spectroscopy was used as a
secondary probe of molecular synthesis to better identify the physical and
chemical processes at play. Our VUV data show that ozone and the azide radical
(N3) are observed in our experiments after electron irradiation of pure O2 and
N2 ices, respectively. Energetic processing of an O2:N2 = 1:1 ice mixture leads
to the formation of ozone along with a series of nitrogen oxides. The electron
irradiation of solid nitrogen oxides, pure and in mixtures, induces the
formation of new species such as O2, N2 , and other nitrogen oxides not present
in the initial ice. Results are discussed here in light of their relevance to
various astrophysical environments. Finally, we show that VUV spectra of solid
NO2 and water can reproduce the observational VUV profile of the cold surface
of Enceladus, Dione, and Rhea, strongly suggesting the presence of nitrogen
oxides on the surface of the icy Saturn moons.
