Low and High Temperature Infrared Spectroscopy of C₆₀and C₇₀Fullerenes

The FT-IR spectra of the fullerenes C60 and C70 have been recorded in the temperature range between 523 K (+250°C) and 93 K (−180°C). As a general rule, it has been observed a shift of the infrared absorption bands toward higher frequencies at lower temperatures. As expected, at 93 K the infrared spectra appear better resolved with sharper absorption bands and higher intensity than the same bands measured at higher temperature. All the infrared spectra of the present study have been made on samples embedded in KBr matrix and all data were extrapolated to 0 K. These spectral data at extremely low temperatures are of paramount importance for astrochemical search of these molecules in space. By comparing the gas phase spectra of both C60 and C70 fullerenes extrapolated to 0 K with the data taken in KBr matrix, the gas phase spectral bands were found systematically shifted 5-10 cm−1 toward higher frequencies than the same bands recorded in KBr. Similarly, the matrix effect is appreciable also when the spectral data taken in KBr are extrapolated to >1000 K. In such case the band position of C60 and C70 fullerenes in the gas phase are shifted to lower frequencies than the extrapolation data taken in KBr matrix.