  We report the linear optical absorption spectra of aluminum clusters Al$_{n}$
(n=2--5) involving valence transitions, computed using the large-scale
all-electron configuration interaction (CI) methodology. Several low-lying
isomers of each cluster were considered, and their geometries were optimized at
the coupled-cluster singles doubles (CCSD) level of theory. With these
optimized ground-state geometries, excited states of different clusters were
computed using the multi-reference singles-doubles configuration-interaction
(MRSDCI) approach, which includes electron correlation effects at a
sophisticated level. These CI wave functions were used to compute the
transition dipole matrix elements connecting the ground and various excited
states of different clusters, and thus their photoabsorption spectra. The
convergence of our results with respect to the basis sets, and the size of the
CI expansion, was carefully examined. Our results were found to be
significantly different as compared to those obtained using time-dependent
density functional theory (TDDFT) [Deshpande \textit{et al. Phys. Rev. B},
2003, \textbf{68}, 035428]. When compared to available experimental data for
the isomers of Al$_{2}$ and Al$_{3}$, our results are in very good agreement as
far as important peak positions are concerned.
  The contribution of configurations to many body wavefunction of various
excited states suggests that in most cases optical excitations involved are
collective, and plasmonic in nature.
