Vibrationally resolved photoelectron spectra were obtained for cold $\mathrm{C}_{70}{}^{-}$ and $\mathrm{C}_{70}{}^{2-}$. Accurate values for the first and second electron affinities (EA’s) of ${\mathrm{C}}_{70}$ were measured as $2.765\pm 0.010$ and ${0.02}_{-0.03}^{+0.01}\mathrm{eV}$, respectively, establishing that $\mathrm{C}_{70}{}^{2-}$ is an electronically stable dianion in the gas phase. The difference between the first and second EA (2.75 eV) provides a direct experimental measure for the on-site Coulomb and exchange interactions between the two excess electrons in $\mathrm{C}_{70}{}^{2-}$. Strong electron correlation effects were also observed between the two excess electrons in $\mathrm{C}_{70}{}^{2-}$.

• Received 20 January 2006

DOI:https://doi.org/10.1103/PhysRevLett.96.143002