ELECTRONIC SHELL ENERGIES AND DEFORMATIONS IN LARGE SODIUM CLUSTERS FROM EVAPORATION SPECTRA

Abundances of sodium clusters resulting from evaporation in vacua of a large ensemble are analyzed quantitatively. Electronic shell structur e gives rise to oscillations in the abundance distributions with maxim a at the shell closings. From this, atomic separation energies and she ll energies are derived from clusters with 50-230 atoms. The experimen tal 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 clus ters with sizes up to 110 electrons. The two quantities are compared a nd found to be nearly identical.