Photoionization of sodium clusters

Abstract

Sodium clusters, Nax (2≤x≤8), were produced in a supersonic jet by coexpansion with argon and subjected to analysis via photoionization coupled with mass spectrometry. The present measurements, made at somewhat higher resolution than earlier literature studies, yield ionization potentials in excellent agreement for x=1 to 4 and x=7, and reveal heretofore unreported structure in the post-threshold spectra. The present measurements enable a more definitive assignment of the ionization potentials, giving a lower value for x=6 and pointing to lower ones for x=5 and 8. The frequently discussed odd–even alternation in ionization potentials is no longer evident beyond the pentamer. Values for the binding energies of Na to Na+x (3≤x≤8) are deduced.