Under standard conditions reaction yields are connected with terms 
like free energy differences and thermal distributions. However, many modern experimental 
techniques, such as supersonic beam expansion or matrix isolation, deal with 
cryogenic temperatures and isolated reactants in inert clusters or solid 
matrices. Under these conditions the photochemical reaction mechanism is in many cases 
strongly dependent on the shape of delocalized initial vibrational or rotational 
wavefunctions of the reactants which can be employed for an efficient 
reaction yield control. Here, we apply, using quantum molecular dynamics simulations,
such a scheme to the rotational control 
of photolysis of the HCl molecule embedded in an icosahedral Ar12 cluster.
First, the HCl molecule is preexcited into a specific low lying 
rotational level. Depending on the rotational state,  the hydrogen probability
is enhanced in different directions within the cluster. In a 
second step, the HCl molecule is photolyzed by a UV pulse. The rapidly 
dissociating hydrogen atom reaches then primarily either the holes in the 
solvent shell or the argon atoms, depending on the rotational preexcitation.
Starting either from the ground or from the first totally symmetric excited
rotational states, the direct dissociation and the delayed process
accompanied with a temporary trapping of the hydrogen atom have
very different relative yields.
As a consequence, differences up to a factor of five in the
temporary population of the hydrogen atom inside the cluster 
after the first hydrogen - cage collision are observed.
In the energy domain a significant 
difference in the structure of the kinetic energy distribution spectra,
connected with the existence of short-lived vibrational resonances
of the hydrogen atom, is predicted.