  A theoretical model for understanding photomagnetism in the heptanuclear
complex $[Mo(IV)(CN)_2(CN-CuL)_6]^{8+}$ perchlorate is developed. It is a
many-body model involving the active orbitals on the transition metal ions. The
model is exactly solved using a valence bond approach. The ground state
solution of the model is highly degenerate and is spanned by five S=0 states,
nine S=1 states, five S=2 states and one S=3 state. The orbital occupancies in
all these states correspond to six $Cu(II)$ ions and one diamagnetic $Mo(IV)$
ion. The optically excited charge-transfer (CT) state in each spin sector occur
at nearly the same excitation energy of 2.993 eV for the physically reasonable
parameter values. The degeneracy of the CT states is largest in the S=3 sector
and so is the transition dipole moment from the ground state to these excited
states. Thus laser irradiation with light of this energy results in most
intense absorption in the S=3 sector. The life-time of the S=3 excited states
is also expected to be the largest as the number of states below that energy is
very sparse in this spin sector when compared to other spin sectors. These twin
features of our model explain the observed photomagnetism in the
$[Mo(IV)(CN)_2(CN-CuL)_6]^{8+}$ complex.
