Carbon clusters investigations

The experimental work reported for carbon clusters ranges from the early investigations of Honig and Drowart on small clusters(1-3) to the recent studies in the groups of Smalley and Kaldor(10-16) on larger clusters with up to 200 atoms. 

In 1984. scientists (Rohlling. Cox. and Caldor at Exxon Research and Engineering) created clusters of carbon (soot) by the laser vaporization of a carbon target rod in connection with a supersonic nozzle. By means of mass spectroscopy, the researchers determined the relative abundance of the carbon clusters produced. Small, 20- to 40-atom clusters of carbon were expected inasmuch as these had been produced a number of times by earlier investigators working on the soot problem. In such experiments, an interesting but unexplained question always arose—Why were only even-numbered carbon clusters produced in the complete absence of odd-numbered clusters See Fig. 3. 

The small target in phase space presented by the Cf0F has led several investigators to propose special kinetic pathways leading directly to C 0F. Some general consideration of carbon clustering can provide a basis for examining the specific proposals. 

The chemisorption cluster studies presented here seem quite encouraging. Cluster investigations are currently under way which address the alkali/carbon monoxide coadsorption problem. 

Our experiments show, unambigously, that a pure carbon film rich with sp linear chains can be formed by assembling carbon clusters at room temperature under ultra-high vacuum. Polyyne and polycumulene species are present and stabilized in all-carbon metastable structures without the need of hetero-atom terminal groups. Under He, N2, and H2 exposure the amount of sp species reduces exponentially with time depending upon the mass of the gas. For the investigated gases no chemical interactions have been observed. 

The [2-1-1] fragmentation of the precursors shown in Figure 6.2 also provides a potential route to monocyclic carbon clusters. Thus cyclic dehydro oligomers of diethynyl[4.4.1]propellatetraenes 6a,b incorporated in a fullerene structure have been prepared and their fragmentation was investigated by mass spectrometry [7]. MALDI TOF mass spectra of 6a,b exhibited peaks due to the stepwise loss of the fullerene fragments, leading to the formation of mono-fullerene adducts of C15 and C20. However, the... 

In this section we shall summarize the results of certain systematic studies we have carried out to aid in the assessment of the performance of DFT methods on various chemical problems. First, computed results for geometries, dipole moments, vibrational frequencies and atomization energies of a set of small molecules will be presented and discussed, followed by an investigation of the reaction barriers of certain radical abstractions. The performance in the latter case is not nearly as good as in the former, and one possible means of improvement of the quality of the DFT barriers is examined. Finally, we give some additional examples of problematic cases, from studies on small carbon clusters important to fullerene chemistry, in which DFT methods were found to have difficulties. 

In spite of the repeated recognition of fullerene-like polymorphs [23-25] it has so far been impossible to isolate them in amounts comparable to those obtained for Ceo and C70. There are only a few studies devoted to the fullerene-like structures, based on elements distinct from carbon or silicon [26-28]. The majority of investigations related to non-carbon clusters has been performed on silicon systems, perhaps because of silicon s applications in the microelectronic industry. 

The correlation of grain size of metal and size of carbon clusters with mechanical properties (hardness, friction, wear) of a-C H,Cu and a-C,(Cu,Zr) films have been investigated. 

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