  In this paper, we present a theoretical investigation of photoabsorption
spectrum of the newly synthesized hydrogenated cluster of aluminium, Al4H6. The
calculations are performed within the wave-function-based semi-empirical method
employing the complete neglect of differential overlap (CNDO) model, employing
a large-scale configuration interaction (CI) methodology, and our results are
found to be in very good agreement with the earlier ones obtained from the ab
initio time-dependent density functional theory (TDDFT). We carefully analyse
the many-particle wave functions of various excited states up to 8 eV, and find
that they are dominated by single-particle band to band excitations. This is in
sharp contrast to bare aluminium clusters, in general, and Al4, in particular,
whose optical excitations are plasmonic in nature. We attribute this difference
to be a consequence of hydrogenation.
