https://doi.org/10.1140/epjd/e2007-00102-1
A quantum chemical approach towards the electronically excited states of helium clusters
1
Department of Physics & Astronomy, University of Leicester, University Road, Leicester, LE1 7RH, UK
2
Forschungszentrum Karlsruhe, Institut für Nanotechnologie, 76021 Karlsruhe, Germany
Corresponding author: a kvh6@le.ac.uk
Received:
25
July
2006
Revised:
24
November
2006
Published online:
24
May
2007
We have investigated the electronic energies of the ground and excited
states of an octahedral helium
cluster by quantum chemical ab initio calculations. The excited levels
were calculated for the central atom for a set of different
inter atomic separations. Our approach yields potential energy curves which
are suited to describe a density dependence of the spectral features
as previously observed in photo excitation experiments. The potential
energy curves of the 2s and 2p states show a hump at 
Å caused by the strong perturbation of neighbouring atoms. The
existence of this hump explains the
experimentally observed blue shift and its dependence on the cluster
size or density, respectively.
The potential curves of the higher levels show almost constant
energies. Perturbations of these levels are small, because the overlap
between the Rydberg orbital and the orbitals of the surrounding atoms is
small. This is the case for both small R values
where the Rydberg orbital is well outside the cluster as well as
for large R where the density drastically decreases.
These findings coincide with the
un-shifted features of small clusters observed in experiments.
PACS: 73.22.-f – Electronic structure of nanoscale materials: clusters, nanoparticles, nanotubes, and nanocrystals / 73.61.Ng – Insulators / 31.50.Bc – Potential energy surfaces for ground electronic states / 31.50.Df – Potential energy surfaces for excited electronic states
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2007
