Non-IPR C-60 solids

Films comprising predominantly novel isomers of C-60 [=C-60(nIPR)] have been generated by low energy ion beam deposition of vibronically excited C-60(+) onto graphite followed by selective sublimation of C-60(I-h) from the deposited isomer mixture. The incident ions were generated by electron impact ionization/fragmentation of sublimed C-70. Images of the C-60(nIPR) films obtained by applying atomic force microscopy show aggregates, which we attribute to covalently interlinked C-60 (nIPR) units. The covalent bonds are inferred from the significantly higher thermal stability of the C-60(nIPR) films compared to the C-60(I-h) van der Waals solid-as measured by thermal desorption with mass spectrometric detection of the C-60 mass channel (the only desorbable species). In contrast to the characteristic doublet structure of the occupied valence band in the ultraviolet photoelectron spectrum of pure C-60(I-h), the valence band of C-60(nIPR) films exhibits a triplet feature with the additional peak occurring at a binding energy of similar to 2.6 eV. This is an indicator of the electronic modifications induced by intermolecular bonding. C-60(nIPR) films exhibit a narrower band gap than found for C-60((I-h). They also have significantly different chemical reactivity toward incorporation of thermal energy deuterium atoms. In order to model the experimental photoelectron spectra, various covalently linked oligomers of C-#1809(60)(C-2 upsilon), the second most stable conventional 60-atom fullerene cage, were calculated by means of the density functional theory. These spectral predictions together with analogous previous observations on related fullerene solids such as C-58 lead us to infer that C-60(nIPR) films consist of fullerene cage isomers containing one or more adjacent pentagon pairs, which mediate covalent cage-cage interconnection. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3120287]