Tunneling and reflection above the repulsive Coulomb barrier of fullerene dianions

Isolated fullerene dianions exhibit a repulsive Coulomb barrier towards electron loss. A kinetic energy release distribution of thermionic emission from C 84 2 − has been measured in a velocity map imaging spectrometer and is compared with a detailed-balance model. A key point is the calculation of the transmission probability through and above the barrier. Previously published, a Wentzel-Kramers-Brillouin (WKB) approach included tunneling but disregarded reflection over the barrier. However, the two processes being at the same fundamental quantum level, reflection must be taken into account. We propose a refined model based on the WKB Kemble formula which includes both. • Fullerene dianions exhibit a repulsive Coulomb barrier towards electron loss. • Thermionic emission of this species has been measured. • Most of the electron emission occurs by tunneling. • Tunneling and reflection above the barrier are at the same quantum level. • Generally disregarded, the reflection above the barrier is introduced.