  After ionization of an inner-valence electron of molecules, the resulting
cation-radicals store substantial internal energy which, if sufficient, can
trigger ejection of an additional electron in an Auger decay usually followed
by molecule fragmentation. In the environment, intermolecular Coulombic decay
(ICD) and electron-transfer mediated decay (ETMD) are also operative, resulting
in one or two electrons being ejected from a neighbor, thus preventing the
fragmentation of the initially ionized molecule. These relaxation processes are
investigated theoretically for prototypical heterocycle-water complexes of
imidazole, pyrrole, and pyridine. It is found that the hydrogen-bonding site of
the water molecule critically influences the nature and energetics of the
electronic states involved, opening or closing certain relaxation processes of
the inner-valence ionized system. Our results indicate that the relaxation
mechanisms of biologically relevant systems with inner-valence vacancies on
their carbon atoms can strongly depend on the presence of the electron-density
donating or accepting neighbor, either water or another biomolecule.
