Eur. Phys. J. D (2016) 70: 192
https://doi.org/10.1140/epjd/e2016-70438-4

Regular Article

Adsorption of sodium and cesium on aggregates of C₆₀

¹ Institut für Ionenphysik und Angewandte Physik, University of Innsbruck, Technikerstrasse 25, 6020 Innsbruck, Austria
² Department of Physics, University of New Hampshire, Durham, New Hampshire 03824, USA

^a e-mail: olof.echt@unh.edu

Received: 8 July 2016
Received in final form: 27 July 2016
Published online: 15 September 2016

Abstract

We explore the formation of C₆₀ sodium and C₆₀ cesium complexes in superfluid helium nanodroplets. Anomalies in mass spectra of these doped droplets reveal anomalies in the stability of ions. (C_60)mCs⁺_n ions (_m ≤ 6) are particularly abundant if they contain n = 6m + 1 cesium atoms; (C_60)mCs²⁺_n dications (_m ≤ 3 or 5) are abundant if n = 6m + 2. These findings are consistent with the notion that alkali metal atoms (A) transfer their valence electrons into the three-fold degenerate lowest unoccupied orbital of C₆₀, resulting in particularly stable C₆₀A₆ building blocks. However, (C₆₀₎₄CsCs²⁺_n dications display an entirely different pattern; instead of an expected anomaly at n = 6 × 4 + 2 = 26 we observe a strong odd-even alternation starting at n = 6. Also surprising is the effect of adding one H₂O or CO₂ molecule to (C_60)mCs_n mono- or dications; anomalies shift by two units as if the impurity were acting as an acceptor for two valence electrons from the alkali metal atoms.