ELECTRON SPECTROSCOPIC STUDY ON ELECTRONIC STRUCTURES DEPENDENCE ON FULLERENE NETWORKS

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An existence of linear carbon chain materials called Carbyne has been suggested, but their nature has not been investigated well because of its instability. Carbyne consists of two types compounds called cumulene type and polyyne type. In order to investigate the electronic structures of carbyne, photoelectron spectra of carbyne model compounds have been measured. Molecular orbital (MO) calculation has been performed to estimate the electronic structures of the linear carbon chain compounds of which photoelectron spectra could not be measured because of difficulty of their synthesis.The photoelectron spectra could be interpreted very well with the MO calculation. The highest occupied molecular orbital (HOMO) of both cumulene and polyyne types compounds resides on the linear carbon chain, not on the termination groups that were introduced to stabilize the molecules. The binding energy (ionization potential) of the HOMO decreases as the chain length increases. It was found that when the number of carbon atoms is the same the HOMO level and the heat of formation of cumulene type compounds are larger than those of polyyene type ones.Photoelectron spectra of calcium atom encapsulated fullerenes, two Ca@C82 isomers were measured. The spectra showed intensity oscillation as those of other fullerenes. ab initio calculation suggests their possible structure. The amounts of transferred electrons from the calcium atom to the fullerene cage was estimated to be two.Photoelectron emission measurements from single wall carbon nano tubes and C60 encapsulated tubes were tried, but reliable data have not been obtained yet. The attempts are under the way.