IR spectroscopy of gas-phase C-60(-)

We present the IR spectrum of the gas-phase C-60(-) anion. The C-60(-) 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 C-60. The results show that the higher frequency band is strongly shifted from its position in neutral C-60 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.