In situ high-resolution infrared spectroscopy of a photopolymerized C-60 film

Photopolymerized C-60 film has been studied under a water-vapor-free condition by means of in situ high-resolution (0.25 cm(-1)) Fourier-transform infrared (FT-IR) spectroscopy. It was found that the IR spectrum of a pristine C-60 film changed markedly after 10-h irradiation with a 500 W mercury lamp at a CsI substrate temperature of 27 degrees C, whereas no change in the IR spectrum of the C-60 Im was observed after 20-h irradiation with the lamp at a substrate temperature of 100 degrees 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 C-60 dimer structure is postulated after comparison between the present results and the theoretical IR calculations reported by Adams ct al. [Phys. Rev. B 50, 17 471 (1994)] and Pederson and Quong [Phys. Rev. Lett. 74, 2319 (1995)].