Enhanced Single-Photon Multi-Detachment in Anions of C$_{60}$ and Observation of a Scaling Law

Absolute single-photon multi-detachment cross sections in C$_{60}^-$ have been measured. We observe a large enhancement (2 and 2.5 times for double and triple detachment, respectfully) of the oscillator strength in the anion compared to neutral C$_{60}$. Although the anion spectra is qualitatively similar to that of multi-photoionzation in C$_{60}$, the anion spectra are substantially compressed in photon energy. The effect of the additional screening provided by the excess electron in the anion on the knock-off process is proposed in order to explain the observed energy scaling. We can also deduce from the results that plasmon resonances do not couple strongly into two- and three-electron removal channels in either the anion or the neutral systems, a surprising result given the intrinsic multi-electron character of the plasmon resonances.