  The predominant reason for the damaging power of high-energy radiation is
multiple ionization of a molecule, either direct or via the decay of highly
excited intermediates, as e.g., in the case of X-ray irradiation. Consequently,
the molecule is irreparably damaged by the subsequent fragmentation in a
Coulomb explosion. In an aqueous environment, however, it has been observed
that irradiated molecules may be saved from fragmentation presumably by charge
and energy dissipation mechanisms. Here, we show that the protective effect of
the environment sets in even earlier than hitherto expected, namely immediately
after single inner-shell ionization. By combining coincidence measurements of
the fragmentation of X-ray-irradiated microsolvated pyrimidine molecules with
theoretical calculations, we identify direct intermolecular electronic decay as
the protective mechanism, outrunning the usually dominant Auger decay. Our
results demonstrate that such processes play a key role in charge
delocalization and have to be considered in investigations and models on
high-energy radiation damage in realistic environments.
