Laboratory IR Spectra of the Ionic Oxidized Fullerenes C60O+ and C60OH+

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.