Laboratory IR Spectra of the Ionic Oxidized Fullerenes C 60 O + and C 60 OH .

We present the first experimental vibrational spectra of gaseous oxidized derivatives of C ₆₀ in protonated and radical cation forms, obtained through infrared multiple-photon dissociation spectroscopy using the FELIX free-electron laser. Neutral C ₆₀ O has two nearly iso-energetic isomers: the epoxide isomer in which the O atom bridges a CC bond that connects two six-membered rings and the annulene isomer in which the O atom inserts into a CC bond connecting a five- and a six-membered ring. To determine the isomer formed for C ₆₀ O ⁺ in our experiment─a question that cannot be confidently answered on the basis of the DFT-computed stabilities alone─we compare our experimental IR spectra to vibrational spectra predicted by DFT calculations. We conclude that the annulene-like isomer is formed in our experiment. For C ₆₀ OH ⁺ , a strong OH stretch vibration observed in the 3 μm range of the spectrum immediately reveals its structure as C ₆₀ with a hydroxyl group attached, which is further confirmed by the spectrum in the 400-1600 cm ^-1 range. We compare the experimental spectra of C ₆₀ O ⁺ and C ₆₀ OH ⁺ to the astronomical IR emission spectrum of a fullerene-rich planetary nebula and discuss their astrophysical relevance.