An ESR study of the formation of La@C82 isomers in arc synthesis

An optimum production efficiency for the La@C82 metallofullerene in arc synthesis was investigated by measuring ESR (electron spin resonance) hyperfine splittings. The yield of La@C82 varied sensitively with the pressure of He buffer gas during the arc synthesis. An optimum yield was obtained around 200 Torr, which is similar to those of empty higher fullerenes. The results indicate that the formation of La@C82 (I) is closely proportional to the evaporation rate of a composite rod; the maximum yield of La@C82 (I) was attained at the highest evaporation rate of the rod. Furthermore, the relative abundance of the two La@C82 isomers, I and II, depends on the He pressure used, and the abundance of La@C82 (II) even exceeds that of La@C82 (I) in a pressure region below about 60 Torr.