Electron Affinities of C_{60} and C_{70} and Cooling of Their Anions

We combine cryogenic storage of fullerene anions up to minutes with laser photo-detachment spectroscopy and measure the electron affinities to be 2.684(3) eV for C_{60} and 2.7665(3) eV for C_{70}, which settle long-standing issues concerning these values. We find that C_{70}^{-} cools more efficiently than C_{60}^{-} and that this is due to differences in photon emission from electronically excited states populated by inverse internal conversion (recurrent fluorescence). We also find that intramolecular vibrational redistribution is no longer effective at low internal energies of C_{60}^{-} or C_{70}^{-}. Radiative cooling becomes extremely slow below intramolecular vibrational redistribution decoupling energies of 0.32(2) and 0.13(3) eV for C_{60}^{-} and C_{70}^{-}, respectively.