The present study focuses on the rotational motion of HCl molecules embedded
in an Ar matrix. Assuming the HCl molecules to occupy substitutional sites in 
the fcc lattice, rotational wavefunctions for the vibrational and electronic
ground state are obtained. Both the energetics and the spatial structure of the
wave functions are investigated. While the J=0 and J=1 state show relatively
little matrix effects, all levels for J>=2 are split. A possible control of
the photodissociation dynamics by selection of rotational states of different
spatial orientation is discussed.