Formation and Stability of High-Spin Alkali Clusters

Abstract

Helium nanodroplet isolation has been applied to agglomerate alkali clusters at temperatures of 380 mK. The very weak binding to the surface of the droplets allows a selection of only weakly bound, high-spin states. Here we show that larger clusters of alkali atoms in high-spin states can be formed. The lack of strong bonds from pairing electrons makes these systems nonmetallic, van der Waals-like complexes of metal atoms. We find that sodium and potassium readily form such clusters containing up to 25 atoms. In contrast, this process is suppressed for rubidium and cesium. Apparently, for these heavy alkalis, larger high-spin aggregates are not stable and depolarize spontaneously upon cluster formation.

Submersion of potassium clusters in helium nanodroplets

“…Our findings concur with work by Schulz et al, 20 who investigated potassium cluster ions (n 25) produced by femtosecond photoionization of potassium clusters on helium nanodroplets. Odd-even intensity alternations were observed, along with pronounced maxima at n = 9 and 21.…”

Photoionisaton of pure and doped helium nanodroplets

“…These cluster mass progressions can extended out to masses of thousands of dopant monomers, in particular when the binding of the neutral cluster is weak thereby causing only little shrinkage of the He droplets due to cluster aggregation [107][108][109]. Therefore, small Ak metal clusters are presumably formed in weakly bound high-spin configurations, whereas large clusters observed in mass spectra of heavily doped large He droplets are assumed to be metallic [69,91,110].…”

Wave Packet Dynamics in Triplet States of Na2 Attached to Helium Nanodroplets

“…The highly quantum nature of superfluid 4 He droplets vs. normal fluid 3 He droplets may affect the coupling of the wave packet motion to the droplet. Moreover, exotic high-spin molecules and complexes formed on He droplets have been studied in real time [31][32][33][34][35][36] .…”