  Laboratory experiments are essential in exploring the mechanisms involved in
stardust formation. One key question is how a metal is incorporated into dust
for an environment rich in elements involved in stardust formation (C, H, O,
Si). To address experimentally this question we have used a radiofrequency cold
plasma reactor in which cyclic organosilicon dust formation is observed.
Metallic (silver) atoms were injected in the plasma during the dust nucleation
phase to study their incorporation in the dust. The experiments show formation
of silver nanoparticles (~15 nm) under conditions in which organosilicon dust
of size 200 nm or less is grown. The presence of AgSiO bonds, revealed by
infrared spectroscopy, suggests the presence of junctions between the metallic
nanoparticles and the organosilicon dust. Even after annealing we could not
conclude on the formation of silver silicates, emphasizing that most of silver
is included in the metallic nanoparticles. The molecular analysis performed by
laser mass spectrometry exhibits a complex chemistry leading to a variety of
molecules including large hydrocarbons and organometallic species. The
reactivity of silver atoms/ions with acetylene was also studied in a laser
vaporization source. Key organometallic species, AgnC2Hm (n=1-3; m=0-2), were
identified and their structures and energetic data computed using density
functional theory. This allows us to propose that molecular Ag-C seeds promote
the formation of Ag clusters but also catalyze hydrocarbon growth. Throughout
the article, we show how the developed methodology can be used to characterize
the incorporation of metal atoms both in the molecular and dust phases. The
reported methodology is a demonstration laying down the ground for future
studies on metals of astrophysical interest such as iron.
