Download R. Delaunay

Ion-induced reactivity in cold clusters of
Polycyclic Aromatic Hydrocarbon molecules
R. Delaunay1*, M. Gatchell2, A. Domaracka1, H. Cederquist2, H. Zettergren2,
B.A. Huber1, L. Adoui1 and P. Rousseau1
1
CIMAP, Boulevard Henri Becquerel, BP 5133, 14070 Caen Cedex 05, France
2
Department of Physics, Stockholm University, S-10691Stockholm, Sweden
*
Corresponding author: [email protected]
Polycyclic Aromatic Hydrocarbon molecules (PAHs) consist of fused aromatic carbon
rings, typically with hexagonal benzene-like structure. Due to their astrophysical relevance,
PAHs have been widely studied in the laboratory, particularly by spectroscopic methods, in order
to identify PAHs in astrophysical environments. However, the processes of formation and
growth of PAH in astrophysical environment are still not fully understood [1]. In this context,
ions colliding with clusters of C60 molecules surprisingly induce the formation of C119 [2].
We have studied the interaction of slow singly and multiply charged ions with cold
neutral clusters of PAHs at the low-energy ion beam facility ARIBE in GANIL (Caen, France).
Clusters are produced in a LN2 cooled gas aggregation source and the products of the collisions
are analyzed by time-of-flight mass spectrometry. The analysis shows that, besides the
fragmentation, the interaction leads to the formation of highly reactive species which promptly
react with neighboring molecules before the cluster dissociates (ps timescale). Thus, we observe
a rich distribution of growth products (see Figure 1) [3]. The fast creation of reactive fragments
is due to ion collisions with molecule nuclei, a process specific to ion interaction with matter.
Classical molecular dynamics simulations of the entire collision process, from the ion impact to
the formation of new molecular species, reproduce the essential features of the measured
molecular growth process. These results show that slow ion impact can initiate a growth
mechanism inside of molecular clusters which could be important for the physical chemistry in
planetary atmospheres such as the one of Saturn’s moon Titan where keV O+ bombardment
occurs.
Figure 1: Left panel – Cationic mass spectrum of collisions between 1.2 keV Ar+
and pyrene (C16H10) clusters. Right panel – Zoom in the pyrene dimer region.
[1] A.G.G.M Tielens, Rev. Mod. Phys, 85, 1021 (2013).
[2] H. Zettergren et al., Phys. Rev. Lett., 110, 15501 (2013).
[3] R. Delaunay et al., J. Phys. Chem. Lett., 6, 1536 (2015).