Electronic Structure of Small Fullerenes: Evidence for the High Stability of $C_{32}$

The electronic structure of small fullerenes determined experimentally by anion photoelectron spectroscopy is compared with calculations. A huge mass signal and a large gap of 1.3 eV comparable to the gap of ${\mathrm{C}}_{70}$ have been found for ${\mathrm{C}}_{32}$, indicating that this cluster is the most stable fullerene below ${\mathrm{C}}_{60}$. Also ${\mathrm{C}}_{36}$, ${\mathrm{C}}_{44}$, and ${\mathrm{C}}_{50}$ exhibit large gaps and surprisingly high stabilities. The criteria for the selection of clusters sufficiently stable to form a cluster material are discussed.