| Autor: |
Ehlich, Rudolf, Landenberger, Peter, Prinzbach, Horst |
| Předmět: |
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| Zdroj: |
Journal of Chemical Physics; 10/1/2001, Vol. 115 Issue 13, 2 Diagrams, 7 Graphs |
| Abstrakt: |
Coalescence of C[sub 20](H)[sub n] fullerenes with n=0–4 was studied by laser desorption and ionization in a time-of-flight mass spectrometer (337 nm N[sub 2] excimer laser). The fullerenes were produced by elimination of bromine from extensively brominated dodecahedranes (mixture, mean composition [C[sub 20]H[sub 1]Br[sub 13]]≡Y, and mixtures with somewhat higher hydrogen content [C[sub 20]H[sub 2]Br[sub 12]]≡X) accessible by photobromination of the C[sub 20]H[sub 20] cage hydrocarbon. For Y probes at 80 mJ/cm2 laser fluence, coalescence of the generated C[sub 20] fullerenes was identified as the dominant process providing a series of (C[sub 20])[sub k][sup +] oligomers (k=1–13); there is evidence for the formation of C[sub 60][sup +] from C[sub 20]. 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 C[sub 20]H[sub n]Br[sub m] ions with m ranging from 0 to 18, fullerene coalescence is suppressed. For X probes the only slightly higher hydrogen content inhibits C[sub 20] coalescence; a C[sub 36]H[sub 4][sup +] ion is interpreted as fullerene. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR] |
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