8-Oxoguanine is one of the key products of
indirect radiation damage to DNA by reactive oxygen species.
Here, we describe ionization of this damaged nucleobase and the
corresponding nucleoside and nucleotide in aqueous phase,
modeled by the nonequilibrium polarizable continuum model,
establishing their lowest vertical ionization energies of 6.8.7.0
eV. We thus confirm that 8-oxoguanine has even lower
ionization energy than the parental guanine, which is the
canonical nucleobase with the lowest ionization energy.
Therefore, it can act as a trap for the cationic hole formed by
ionizing radiation and thus protect DNA from further radiation
damage. We also model using time-dependent density functional
theory and measure by liquid jet photoelectron spectroscopy 
the valence photoelectron spectrum of 8-oxoguanine in water. We
show that the calculated higher lying ionization states match 
well the experiment which, however, is not sensitive enough to
capture the electron signal corresponding to the lowest ionization 
process due to the low solubility of 8-oxoguanine in water.