Electronic shell energies and deformations in large sodium clusters from evaporation spectra

Abundances of sodium clusters resulting from evaporation in vacuo of a large ensemble are analyzed quantitatively. Electronic shell structure gives rise to oscillations in the abundance distributions with maxima at the shell closings. From this, atomic separation energies and shell energies are derived from clusters with 50--230 atoms. The experimental shell energies are 2--3 times smaller in amplitude than calculated theoretically for spherical clusters. The discrepancy is understood as the result of deformations of the nonmagic clusters. In addition, the energy oscillations due to shell structure are extracted from (i) the atomic separation energies and (ii) the ionization potentials of clusters with sizes up to 110 electrons. The two quantities are compared and found to be nearly identical.