High-resolution photoelectron imaging of cold C₆₀⁻ anions and accurate determination of the electron affinity of C₆₀.

High-resolution photoelectron imaging and spectroscopy of cold C₆₀⁻ anions are reported using a newly built photoelectron imaging apparatus coupled with an electrospray ionization source and a temperature-controlled cryogenic ion trap. Vibrationally resolved photoelectron spectra are obtained for the detachment transition from the ground state of C₆₀⁻ to that of C60 at various detachment wavelengths from 354.84 nm to 461.35 nm. The electron affinity of C60 is accurately measured to be 2.6835 ± 0.0006 eV. Numerous unexpected vibrational excitations are observed in the photoelectron spectra due to the Jahn-Teller effect in C₆₀⁻ and Hertzberg-Teller vibronic coupling in both C₆₀⁻ and C60. Both the relative intensities of vibrational peaks and their photoelectron angular distributions provide evidence for the vibronic couplings. The observed p-wave-like behavior in the angular distribution of the 0₀⁰ transition suggests that the electron is detached from an s-type orbital.