Magic Numbers for Packing Adamantane in Helium Droplets: Cluster Cations, Dications, and Trications

We
report the first observation of cations, dications, and trications
of large clusters of adamantane. Cluster formation was initiated near
0 K in helium droplets and ionization was achieved with one or more
collisions with energetic He species (He*, He+, or He*–). The occurrence of Coulomb explosion appeared to
discriminate against the formation of small multiply-charged clusters.
High-resolution mass spectrometry revealed the presence of “magic
number” m/z peaks that can
be attributed to the packing of adamantane molecules into cluster
structures of special stability involving preferred arrangements of
these molecules. These abundance anomalies were seen to be independent
of charge state. While some dehydrogenation of adamantane and its
clusters was seen as well, no major transformations into adamantoids
or microdiamonds were observed.