Coalescence of C20 fullerenes

Abstract

Coalescence of C20(H)n fullerenes with n=0–4 was studied by laser desorption and ionization in a time-of-flight mass spectrometer (337 nm N2 excimer laser). The fullerenes were produced by elimination of bromine from extensively brominated dodecahedranes (mixture, mean composition [C20H1Br13]≡Y, and mixtures with somewhat higher hydrogen content [C20H2Br12]≡X) accessible by photobromination of the C20H20 cage hydrocarbon. For Y probes at 80 mJ/cm2 laser fluence, coalescence of the generated C20 fullerenes was identified as the dominant process providing a series of (C20)k+ oligomers (k=1–13); there is evidence for the formation of C60+ from C20. At lower fluences (30 mJ/cm2) in the mass spectra measured near the desorption threshold or in the low ion velocity regime, the bromine substituents were not (totally) eliminated, the original degree of bromination has even been raised. High laser fluences (1500 mJ/cm2) primarily effect the bromine content, generating C20HnBrm ions with m ranging from 0 to 18, fullerene coalescence is suppressed. For X probes the only slightly higher hydrogen content inhibits C20 coalescence; a C36H4+ ion is interpreted as fullerene.

Theoretical study of the nucleation/growth process of carbon clusters under pressure

“…[21][22][23] It should be noted that our strong topological dependence on density rather than temperature does not agree with the results of Yamaguchi et al who used a tight binding molecular dynamics ͑TBMD͒ scheme and found a strong temperature influence on the topologies, but little influence of the density: for similar starting configurations at 1000 K, they obtained a density-independent mixture of sp and sp 2 structures consisting mainly of flat graphitic "flakes" connected by carbon chains. Their graphitic flakes were only curved at higher temperatures, which allowed the formation of large fullerene structures.…”

C20 Carbon Clusters: Fullerene–Boat–Sheet Generation, Mass Selection, Photoelectron Characterization

“…Extreme reactivity of cage 1 due to the Jahn-Teller effect, which led to a mixture of rapidly interconverting geometries of nearly equal energies, [6] was demonstrated in laser desorption experiments with 12: 1 rapidly coalesced to give a series of (C 20 ) k + oligomers (k = 2-13), presumably via [2 + 2]cycloadditions. [6,57] Extensive computations have subsequently been devoted to the potentially superconducting properties of the condensed phases of 1 [58] and [-FeC 20 -] polymers, [59] to electron scattering from 1, [60] to 1 as cap of very narrow nanotubes, [61] as guest in huge fullerenes, [62] as host for encapsulated gases, [63] and as ligand in h 5 -p complexes with transition metals. [64] There remain uncertainties for the graphitic clusters 4 and 4H 2 .…”

Theoretical Studies on the Smallest Fullerene: from Monomer to Oligomers and Solid States

“…[16] Furthermore, (C 20 ) þ k oligomers (k = 1±13), formed by coalescence of C 20 cages, have been identified experimentally. [17] Most recently, the C 20 [2+2] cycloaddition dimerization mechanism was elucidated theoretically. [18] This new C 20 cage building block for organic solids poses many questions.…”