Ions colliding with clusters of fullerenes - Decay pathways and covalent bond formations

The following article appeared in Journal of Chemical Physics 139.3 (2013): 034309 and may be found at http://scitation.aip.org/content/aip/journal/jcp/139/3/10.1063/1.4812790We report experimental results for the ionization and fragmentation of weakly bound van der Waals clusters of n C60 molecules following collisions with Ar2+, He2+, and Xe20+ at laboratory kinetic energies of 13 keV, 22.5 keV, and 300 keV, respectively. Intact singly charged C60 monomers are the dominant reaction products in all three cases and this is accounted for by means of Monte Carlo calculations of energy transfer processes and a simple Arrhenius-type [C60]n+ → C60++(n-1) C60 evaporation model. Excitation energies in the range of only ∼0.7 eV per C60 molecule in a [C60]13 + cluster are sufficient for complete evaporation and such low energies correspond to ion trajectories far outside the clusters. Still we observe singly and even doubly charged intact cluster ions which stem from even more distant collisions. For penetrating collisions the clusters become multiply charged and some of the individual molecules may be promptly fragmented in direct knock-out processes leading to efficient formations of new covalent systems. For Ar2 + and He2 + collisions, we observe very efficient C119+ and C118+ formation and molecular dynamics simulations suggest that they are covalent dumb-bell systems due to bonding between C59+ or C58+ and C60 during cluster fragmentation. In the Ar 2+ case, it is possible to form even smaller C120-2m+ molecules (m = 2-7), while no molecular fusion reactions are observed for the present Xe20+ collisionsThis work was supported by the Swedish Research Council (Contract Nos. 621-2008-3773, 621-2009-3468, and 621- 2011-4047). The authors thank Fabien Noury and Stephane Guillous for supplying the ion beam. We acknowledge the COST action CM1204 “XUV/X-ray light and fast ions for ultrafast chemistry (XLIC)” and computer time from CCCUAM and BSC Mare Nostrum. Work partially supported by Project Nos. FIS2010-15127, CTQ2010-17006, CSD2007- 00010 (MICINN), S2009/MAT1726 (CAM), and the CNRS PICS-05356. Studies of interstellar chemistry at Leiden Observatory are supported through advanced-ERC grant (Grant No. 246976) from the European Research Council, through a grant by the Dutch Science Agency, NWO, as part of the Dutch Astrochemistry Network, and through the Spinoza premie from the Dutch Science Agency, NW