We have examined the infrared (IR) spectra of electron-beam (EB) irradiated C60 films, using in situ IR spectroscopy in the temperature range of 60–300 K. The irradiation-time evolution of the IR spectra shows that two highly intense new peaks finally appear around 565 and 1340 cm−1 when the EB-induced C60 polymerization was saturated. To determine the cross-linked structure of the polymer explicitly, we have compared the IR spectra with theoretical spectra obtained from the cross-linked structure of all C120 stable isomers derived from the general Stone–Wales (GSW) rearrangement, using first-principles density-functional calculations. Since each C120 isomer has the same cross-linked structure as that of its corresponding one-dimensional (1D) C60 polymer, the IR modes obtained from the cross-linked structure of C120 are close to those obtained from the corresponding 1D polymer. Comparison between the experimental and theoretical IR spectra suggests that the 1D peanut-shaped C60 polymer has a cross-linked structure roughly similar to that of the P08 peanut-shaped C120 isomer.

A 3 kV electron-beam irradiation of a C60 film gives rise to formation of one-dimensional (1D) uneven peanut-shaped C60 polymer with a cross-linked structure close to that of the P08 C120 stable isomer obtained from the general Stone–Wales rearrangement. In this study, we examined the evolution of infrared (IR) spectra of C60 films with respect to electron beam (EB) irradiation time, using in situ high-resolution IR spectroscopy and first-principles density-functional calculations, and found semi-quantitatively that the 1D uneven peanut-shaped C60 polymer is formed via intermediate polymers with a cross-linkage close to that of P04 and P06 C120 isomers obtained from GWS rearrangement. In addition, we examined the dependence of EB-induced C60 polymerization on an incident energy of EB in the range 3–7 kV. IR spectra obtained for 5 and 7 kV EB irradiation of C60films showed the same product as for 3 kV EB irradiation. However, when 5 and 7 kV EBs continued to irradiate C60 films for a long time after the polymer formation, the 1D peanut-shaped polymer did not proceed to become 1D polymers with a more coalesced linkage than that of the P08 one but was destroyed to become amorphous carbons.

A one-dimensional (1D) uneven peanut-shaped C(60) polymer formed from electron-beam (EB)-induced polymerization of C(60) molecules showed an anomalous increase in two characteristic infrared (IR) peak intensities, which are respectively due to the radial and tangential motion of the 1D polymer, when compared to the IR peaks of pristine C(60) films. This anomaly was analyzed on the basis of the vibrational van Hove singularity (VHS), using an extended thin-shell elastic model fully considering the effects of periodic radius modulation inherent to the 1D uneven peanut-shaped C(60) polymer. We succeeded in explaining the enhancement in the tangential peak intensity by VHS, whereas the origin to cause that in the radial peak intensity is still unclear.

ABSTRACT:The electronic properties, in particular the role of 7-and 8-membered rings in the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gap, of stable C 120 isomers derived from the general Stone-Wales rearrangement have been investigated using the discrete-variational X␣ MO method. It is found that the adjacent 7-membered rings located in the waist region of the isomers tend to have positive effective charges, and that the electron polarization induced by the adjacent 7-membered rings makes the HOMO level higher, which reduces the HOMO-LUMO gap of the C 120 isomers.

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