  The linear optical absorption spectra of three isomers of planar boron
cluster B$_{13}$ are calculated using time-dependent spin-polarized density
functional approach. The geometries of these cluster are optimized at the
B3LYP/6-311+G* level of theory. Even though the isomers are almost degenerate,
the calculated spectra are quite different, indicating a strong
structure-property relationship. Therefore, these computed spectra can be used
in the photo-absorption experiments to distinguish between different isomers of
a cluster.
