Thermionic emission in small carbon cluster anions

Photodetachment of mass-selected small Cn− clusters has been studied by photoelectron imaging spectroscopy. As in small refractory metal cluster anions, the low kinetic energy spectrum is dominated by thermionic emission. However, the effective temperatures measured from the electron kinetic energy spectra are sensibly larger than expected assuming complete thermal equilibrium. This discrepancy, more significant than in metal clusters, is attributed to the presence of a large gap in the density-of-states, which precludes a complete thermal equilibrium in the excited species before decay.