IR spectroscopy of gas-phase C60-.

We present the IR spectrum of the gas-phase C60(-) anion. The C60(-) anions are mass-selected and trapped in an ion cyclotron mass spectrometer cell. The spectrum is obtained by recording the yield of electrons following infrared multiple photon absorption and subsequent electron detachment of the anions. Two bands are observed that correlate to two of the four IR-allowed transitions in neutral C60. The results show that the higher frequency band is strongly shifted from its position in neutral C60 and is a sensitive marker for the charge state. The band positions and intensities are compared to results obtained by theory as well as to known bands in solid samples and good agreement is found.