Vaporization of graphite

Preliminary experiments with contact-arc vaporization of graphite in a stream of He containing N2 or NH3 yielded nitrogen-containing products tentatively assigned to species such as C70N2 and (x = 2, 4, 6)... 

There are several methods in use for producing these clusters. Particle bombardment or laser vaporization of a graphite surface leads to direct formation of ions that can be detected by mass spectrometry. These are normally of relatively small size (n<30). By laser vaporization of graphite into a molecular beam neutral... 

The Wlc total atomization energy at 0 K of aniline, 1468.7 kcal/mol, is in satisfying agreement with the value obtained from heats of formation in the NIST WebBook 39), 1467.7 0.7 kcal/mol. (Most of the uncertainty derives from the heat of vaporization of graphite.) The various contributions to this result are (in kcal/mol) SCF limit 1144.4, valence CCSD correlation energy limit 359.0, connected triple excitations 31.7, inner shell correlation 7.6, scalar relativistic effects -1.2, atomic spin-orbit coupling -0.5 kcal/mol. Extrapolations account for 0.6, 12.1, and 2.5 kcal/mol, respectively, out of the three first contributions. 

In 1984 it was observed that, upon laser vaporization of graphite, large carbon-only clusters C with u = 30-190 can be produced [14]. The mass distribution of these clusters was determined by time-of-flight mass spectrometry. Only ions with... 

Figure 1.3 Time-of-flight mass spectrum of carbon clusters produced by laser vaporization of graphite under the optimum conditions for observation of a dominant Ceo signal [15].

Fullerene generation by vaporization of graphite or by combustion of hydrocarbons is very effective and certainly unbeatable what facile production in large quantities is concerned. However, total synthesis approaches are attractive because (a) specific fullerenes could be made selectively and exclusively, (b) new endohedral fullerenes could be formed, (c) heterofullerenes and (d) other cluster modified fullerenes could be generated using related synthesis protocols. 

Before that time, experimental evidence for the existence of heterofullerenes was very rare. In 1991 Smalley and co-workers [4,5] reported on the mass spectrometric detection of borafullerenes C5q B (n = 1-6) generated by laser vaporization of graphite-boron nitride composites. Later, in the same year, the preparation of several clusters was reported [6-8]. However, none of these species has been isolated or structurally characterized. In 1994 Clemmer et al. presented evidence for heterofullerenes containing a metal as part of the framework [9]. Muhr etal. reported on the preparation of monoborafullerenes however, presumably due to the instability of these systems, no pure material could be isolated and completely characterized [10]. Real preparative heterofullerene chemistry began in 1995. The... 

So far, all efforts to generate, isolate and characterize heterofuUerenes via Kratsch-mer-Huffman vaporization of graphite in the presence of hetero-element-containing compounds such as boron nitride (BN) or cyanogen (CN)2 have failed. An alternative route for the direct formation of heterofuUerenes is cluster rearrangement within exohedral fullerene derivatives such as iminofullerenes and azafuUeroids. The first hints of success by this approach were obtained from mass spectrometry investigations of the cis-l-diazabishomo[60]fullerene 3 [12], the n-butylamine adduct 4 [12] the 1,2-epiminofullerene 5 [11] and the cluster opened ketolactam 6 [2]. 

Fullerenes were detected for the first time upon laser-induced vaporization of graphite [10]. However, the first preparative method involved the vaporization of graphite by arc discharge (see Fig. 4) [30-33]. Today, the sooting flame from a... 

The IR spectrum of 133 was obtained by laser vaporization of graphite and subsequent condensation of the reaction products in solid argon at 10 K. However, only the most intense mode at 1695 cm could be detected. " The antisymmetric stretching vibration of the linear isomer 132 is observed at 1952 cm . " " The assignment could be corroborated by measuring the spectra of isotopically labeled compounds. In a more recent theoretical work, the UV spectra of 133 and 134 were calculated, " " but experimental data are lacking so far. 

Here, AHsub is the heat of sublimation (direct vaporization) of graphite, Affdiss is the bond energy of molecular hydrogen, and the energies are quoted in kilojoules per mole. 

Figure 5. Mass spectrum of carbon clusters (C3-C100) generated by laser vaporization of graphite (Rohlfing el al. 1984). (Reprinted with permission of the American Institute of Physics.)...

The synthesis of the dicyanopolyynes can be achieved by vaporization of graphite in the presence of cyanogen. The smaller chains (8-18 C atoms) can be separated by extraction with toluene and then chromatography. The materials with longer chains (500 or more C atoms) are also soluble in most organic solvents. 

Figure 2 Time-of-flight mass spectrum of carbon clusters produced by laser vaporization of graphite (September 4, 1985) imder conditions which first exhibited the dominance of the Cgo cluster and led to the recognition that 60 might be a magic number. (Reprinted with permission from Ref 2a. 1991 American Chemical Society)...

Figure 3 Photograph (by transmitted Ught) of the fullerene crystals formed by gentle evaporation of the red/brown benzene extract from soot produced by the arc vaporization of graphite. (Reprinted with permission of MacmiUan from W. Kratschmer et al. )...

Heath, J.R., Zhang, Q., Obrien, S.C. et al. (1987) The formation of long carbon chain molecules during laser vaporization of graphite. Journal of the American Chemical Society, 109, 359-363. 

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