  We study the carbon-dope aluminum clusters by using time-of-flight mass
spectrum experiments and {\em ab initio} calculations. Mass abundance
distributions are obtained for anionic aluminum and aluminum-carbon mixed
clusters. Besides the well-known magic aluminum clusters such as Al$_{13}^-$
and Al$_{23}^-$, Al$_7$C$^-$ cluster is found to be particularly stable among
those Al$_n$C$^-$ clusters. Density functional calculations are performed to
determine the ground state structures of Al$_n$C$^-$ clusters. Our results show
that the Al$_7$C$^-$ is a magic cluster with extremely high stability, which
might serve as building block of the cluster-assembled materials.
