Ordered phases of ethylene adsorbed on charged fullerenes and their aggregates

Abstract

In spite of extensive investigations of ethylene adsorbed on graphite, bundles of nanotubes, and crystals of fullerenes, little is known about the existence of commensurate phases; they have escaped detection in almost all previous work. Here we present a combined experimental and theoretical study of ethylene adsorbed on free C60 and its aggregates. The ion yield of (C60)m(C2H4)n+ measured by mass spectrometry reveals a propensity to form a structurally ordered phase on monomers, dimers and trimers of C60 in which all sterically accessible hollow sites over carbon rings are occupied. Presumably the enhancement of the corrugation by the curvature of the fullerene surface favors this phase which is akin to a hypothetical 1 × 1 phase on graphite. Experimental data also reveal the number of molecules in groove sites of the C60 dimer through tetramer. The identity of the sites, adsorption energies and orientations of the adsorbed molecules are determined by molecular dynamics calculations based on quantum chemical potentials, as well as density functional theory. The decrease in orientational order with increasing temperature is also explored in the simulations whereas in the experiment it is impossible to vary the temperature.

Cold physics and chemistry: Collisions, ionization and reactions inside helium nanodroplets close to zero K

“…One way to count the number of molecules in the groove region is by plotting the cumulative sum  of molecules that lie in the midplane of the dimer versus the distance from the dimer axis. The plateau in the bottom trace in Figure 61 indicates that 6 C2H4 molecules lie in the groove region, in agreement with experiment [587]. The inset in Figure 61 illustrates the structure of the C60 dimer with all groove sites being filled.…”

“…N2, O2 and CH4 show steps at n = 7, C2H4 at 6, and CO2 at 8. Theoretical studies of CH4 [372,586], C2H4 [587], and CO2 [584] reveal that this feature has a common origin; it reflects the number of molecules in the groove region. These molecules are more strongly bound than other molecules in the first layer because they are in close proximity with two fullerenes.…”

Adsorption of helium on isolated C60and C70anions

“…However, theoretical studies leave no doubt that 32 helium atoms form a commensurate 1 × 1 phase on neutral or positively charged C 60 [11,13,14]. The same is true for adsorption of methane [24], ethylene [25], and xenon [28] but neither for neon, argon, and krypton [28] nor for polar molecules [29].…”

“…At the same time, curvature increases the distance between atoms adsorbed at hollow sites to an extent that not only helium but even larger particles (including hydrogen, methane, ethylene or nitrogen) can be accommodated in the 1 × 1 phase of C 60 , with one particle each at the centres of the 12 pentagons and 20 hexagons (25 hexagons for C 70 ) [19,22,24,25], for a review see [12]. The anomaly at n = 32 also appeared in mass spectra of C 60 that was allowed to react in a gas aggregation cell with red phosphorous [26] or alkaline earth metals [27].…”

On enhanced hydrogen adsorption on alkali (cesium) doped C60 and effects of the quantum nature of the H2 molecule on physisorption energies

“…Dissociation energies are given in Table 2 H2 prefers to adsorb on C60Cs + in such a way that it maximizes its polarization interaction with Cs + and its van der Waals interaction with C60 (see Figure 4) which results in De = 0.110 eV (D0 = 0.061 eV). We call this a groove site (Figure 4c) in analogy to the grooves between two or more fullerenes/nanotubes [58,59]. Marginally smaller values of De = 0.080 eV are reached outside the groove near Cs.…”