Formations of DumbbellC118andC119inside Clusters ofC60

Abstract

We report highly selective covalent bond modifications in collisions between keV alpha particles and van der Waals clusters of C 60 fullerenes. Surprisingly, C 119 þ and C 118 þ are the dominant molecular fusion products. We use molecular dynamics simulations to show that C 59 þ and C 58 þ ions-effectively produced in prompt knockout processes with He 2þ -react rapidly with C 60 to form dumbbell C 119 þ and C 118 þ . Ion impact on molecular clusters in general is expected to lead to efficient secondary reactions of interest for astrophysics. These reactions are different from those induced by photons. DOI: 10.1103/PhysRevLett.110.185501 PACS numbers: 61.48.Àc, 31.15.xv, 36.40.Qv Photodriven intracluster reactions have been observed in clusters of fullerenes [1,2] and in, e.g., clusters of methanol, water, dimethyl ether, and acetic acid molecules [3]. Clusters of fullerenes are of particular interest in this context as C 60 and C 70 recently have been observed in space [4,5] at temperatures indicating that they may reside on grains [4] or are in the solid phase (fullerite) [6]. The question of how fullerenes form in space and elsewhere [7][8][9] is still open and here we report experimental observations on specific very efficient fullerene growth processes inside small pieces of fullerite material. These ion-impact induced growth processes in which so-called dumbbell fullerene systems are formed are inherently different from the ones induced by photons [1,2] for reasons that will be discussed in the following.The lowest energy barrier for formation of covalently bound dumbbell C 120 from two neutral C 60 molecules is roughly one or two electron volts [10]. Thus, two C 60 molecules in their ground states may, in principle, form such a C 120 system when the center-of-mass kinetic energy is larger than this barrier. However, molecular dynamics simulations by Jakowski, Irle, and Morokuma [11] have shown that, in practice, much larger kinetic energies are needed to form dumbbell C 120 (* 60 eV) or single-cage C 120 (*100 eV) efficiently [11]. The reason is that at least one C 60 cage needs to rearrange to form covalent bonds with the other cage on very short, picosecond, time scales. This is highly unlikely in a single encounter at low kinetic energy, as the transferred energy is redistributed over the fullerene molecule and a critical energy needs to be localized in a specific bond in order to break it. On the other hand, the reverse reaction (dissociation) may proceed at much lower energies but after many vibrations and on much longer time scales. For C 60 -C 60 collisions at kinetic energies above 60/100 eV covalent bond formation becomes much more likely but will then also give internally hot dumbbell/single-cage C 120 . Single-cage C 120 will fragment through sequences of C 2 emissions yielding molecular mass distributions with an even number of carbon atoms [1] as C 2 loss is the lowest-energy dissociation channel at about 10 eV. The dumbbell C 120 ! C 60 þ C 60 dissociation energy is only a couple of eV [1...

Laboratory Formation and Photochemistry of Fullerene/Anthracene Cluster Cations

“…Dunk et al (2013) also reported the formation of fullerene cluster cations resulting from the gas-phase interaction of C 60 and C 70 with coronene (C 24 H 12 ) molecules under energetic conditions. In addition, laboratory studies of processing of van der Waals clusters of PAHs and of fullerenes in the gas phase by energetic ions (e.g., 24 keV O 2+ or 12 keV Ar 2+ ) have revealed the formation of chemically bonded large species through direct knock-out of carbon atoms (Zettergren et al 2010(Zettergren et al , 2013Delaunay et al 2015).…”

Growth, thermal desorption and low dose ion bombardment damage of C60 films deposited on Cu(111)

“…Despite damage on C 60 films under ion bombardment having been previously studied, most of these works were focused on high incoming energies (>20 keV), high irradiation doses or different incoming projectiles [33][34][35][36][37][38][39][40][41][42]. The modification of fullerene films using ion beams in the LEIS regime (ion energy <10 keV) has barely been studied [43][44][45][46][47]; focusing mostly on Ar + incoming projectiles.…”

“…The modification of fullerene films using ion beams in the LEIS regime (ion energy <10 keV) has barely been studied [43][44][45][46][47]; focusing mostly on Ar + incoming projectiles. Among these articles, it is relevant to mention that a direct knock-out of a single carbon atom from C 60 molecules have been observed for high impact energies (>13.5 keV) of Ar 2+ and He 2+ collisions on C 60 molecular clusters, leading this process to an efficient formation of new systems like + C , [42,48]. In the present work we studied the growth and thermal stability of C 60 films on Cu(111) as an extension of a previous research were we studied the growth of C 60 on Cu(111) with AES and kinetic Monte Carlo simulations [8].…”

Laboratory Photochemistry of Covalently Bonded Fluorene Clusters: Observation of an Interesting PAH Bowl-forming Mechanism

“…Afterwards, the reaction between PAH radicals and PAHs leads to covalently bonded clusters (Le Page et al 2001;Richter & Howard 2000;Richter et al 2005). Finally, we point towards experimental studies on the interaction of energetic ions with PAH clusters which also lead to covalently bonded PAH-multimers (Zettergren et al 2013;Gatchell et al 2015;Gatchell & Zettergren 2016).…”