  Irradiation-driven fragmentation and chemical transformations of molecular
systems play a key role in nanofabrication processes where organometallic
compounds break up due to the irradiation with focused particle beams. In this
study, reactive molecular dynamics simulations have been performed to analyze
the role of the molecular environment on the irradiation-induced fragmentation
of molecular systems. As a case study, we consider the dissociative ionization
of iron pentacarbonyl, Fe(CO)$_5$, a widely used precursor molecule for focused
electron beam-induced deposition. In connection to recent experiments, the
irradiation-induced fragmentation dynamics of an isolated Fe(CO)$_5^+$ molecule
is studied and compared with that of a Fe(CO)$_5^+$ molecule embedded into an
argon cluster. The appearance energies of different fragments of an isolated
Fe(CO)$_5^+$ agree with the recent experimental data. For Fe(CO)$_5^+$ embedded
into an argon cluster, the simulations reproduce the experimentally observed
suppression of Fe(CO)$_5^+$ fragmentation and provide an atomistic-level
understanding of this effect. Understanding irradiation-driven fragmentation
patterns for molecular systems in environments facilitates the advancement of
atomistic models of irradiation-induced chemistry processes involving complex
molecular systems.
