Probing the Angular Momentum Character of the Valence Orbitals of Free Sodium Nanoclusters
C. Bartels,
C. Hock,
J. Huwer,*
R. Kuhnen,
J. Schwöbel,
B. von Issendorff
Although many properties of polyatomic metal clusters have been
rationalized by an electron shell model resembling that used
for free atoms, it remained unclear how reliable this analogy
is with respect to the angular momentum eigenstate character
of the electronic wave functions. We studied free size-selected
negatively charged clusters of sodium atoms (Na
n–) of
approximately spherical shape (
n = 19, 40, 55, 58, 147) by angle-resolved
photoelectron spectroscopy over a broad range of photon energies
(1.5 to 5 electron volts). Highly anisotropic, state- and energy-dependent
angular distributions emerged for all sizes. Well-defined classes
of energy dependence related to the approximate angular momenta
of the bound-state orbitals indicate that the overall character
of the valence electron wave functions is not appreciably influenced
by the interaction with the ion background. The measured distributions
nevertheless deviate strongly from the predictions of single-electron
models, hinting at a distinct role of correlated multielectron
effects in the photoemission process.
* Present address: ICFO–Institut de Ciències Fotòniques, Mediterranean Technology Park, 08860 Castelldefels (Barcelona), Spain.
Present address: Institut für Angewandte Physik und Zentrum für Mikrostrukturforschung, Jungiusstraße 9a, 20355 Hamburg, Germany.
To whom correspondence should be addressed. E-mail: bernd.von.issendorff{at}uni-freiburg.de
