Electronic and vibrational spectra of fullerenes in contact with oxygen

The high-resolution electronic and vibrational spectra of fullerenes C-60, C-70, and C-78 were analyzed. The absorption spectrum of fullerene C-60 contains a series of seven well-resolved bands in the range 200-280 nm, the strongest of them being at 240 nm, as well as two broadened bands of lower intensity at 280 and 330 nm. The former seven bands were assigned to vibrationally excited pi-pi* transitions in the molecular system of conjugated pi bonds, and the latter two, to intermolecular interactions in a fullerene-oxygen contact complex. As the molecular weight of the fullerene increases, the short-wave absorption band suffers a hypsochromic shift, which is characteristic of nonalternant aromatic systems. The IR spectra provide evidence for the formation of a contact charge-transfer complex with oxygen by displaying emission and absorption in the region of fundamental frequencies of the triplet, singlet, radical-ion, and ionic states of molecular oxygen.