In situhigh-resolution infrared spectroscopy of a photopolymerizedC60film

Photopolymerized ${\mathrm{C}}_{60}$ film has been studied under a water-vapor-free condition by means of in situ high-resolution (0.25 ${\mathrm{cm}}^{-1\mathrm{}}$) Fourier-transform infrared (FT-IR) spectroscopy. It was found that the IR spectrum of a pristine ${\mathrm{C}}_{60}$ film changed markedly after 10-h irradiation with a 500 W mercury lamp at a CsI substrate temperature of 27 °C, whereas no change in the IR spectrum of the ${\mathrm{C}}_{60}$ film was observed after 20-h irradiation with the lamp at a substrate temperature of 100 °C. Compared with the previous FT-IR result reported by Rao et al. [Science 259, 955 (1993)], the present IR spectra for the photopolymerized film had many new peaks and the peaks corresponding to the four intrinsic intensive IR-active modes were split. A ${\mathrm{C}}_{60}$ dimer structure is postulated after comparison between the present results and the theoretical IR calculations reported by Adams et al. [Phys. Rev. B 50, 17 471 (1994)] and Pederson and Quong [Phys. Rev. Lett. 74, 2319 (1995)].