  A model for determining the hyperfine structure of the excited electronic
states of diatomic bialkali heteronuclear molecules is formulated from the
atomic hyperfine interactions, and is applied to the case of bosonic $^{39}$KCs
and fermionic $^{40}$KCs molecules. The hyperfine structure of the potential
energy curves of the states correlated to the
K($4s\,^2S_{1/2}$)+Cs($6p\,^2P_{1/2,3/2}$) dissociation limits is described in
terms of different coupling schemes depending on the internuclear distance $R$.
These results provide the first step in the calculation of the hyperfine
structure of rovibrational levels of these excited molecular states in the
perspective of the identification of efficient paths for creating ultracold
ground-state KCs molecules.
