Low Temperature Infrared Spectroscopy of C60 and C70 Fullerenes and Fullerane C60H18

Abstract

The FT-IR spectra of the fullerenes C60 and C70, the fullerane C60H18 and the fullerane mixture C60Hx (77%) and C70Hy (22%) with x ≈ y > 36–38 have been taken in the range of temperatures comprised between +250°C (523 K) and −180°C (93 K). For all the samples studied, as general rule, it has been observed a shift of the infrared absorption bands toward higher frequencies at lower temperatures although some exceptions have been identified. The C–H stretching bands of fulleranes appear almost independent from the temperature and this is of extreme importance from the astrochemical point of view for the search of these molecular species in space. As expected, at 93 K the infrared spectra appear better resolved with absorption bands more sharp and of 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, it has been found that at 0 K the entity of the band shift due to matrix effect is 5–10 cm−1 toward lower frequencies. In other words, the gas phase spectral bands are systematically shifted 5–10 cm−1 toward higher frequencies than the same bands recorded in KBr. Instead, the matrix effect becomes quite negligible when the spectral data taken in KBr are extrapolated to >1,000 K. In such case there is a fair agreement between the band position of C60 and C70 fullerenes in the gas phase and the extrapolation from data taken in KBr matrix.