Photolysis of the HCl molecule surface solvated on clusters with two to twelve argon atoms
is investigated by means of quantum molecular dynamics simulations. Two basic
questions are addressed: i) How does the cage effect change upon increasing the size
of the cluster, and ii) How can caging be influenced by an IR excitation of
HCl hindered rotation (libration) prior to UV photolysis. The efficiency of caging
is discussed in terms of measurable quantities. In the time domain, temporary populations
of the trapped hydrogen atom are monitored, while in the energy domain 
short-lived vibrational resonances are observed as a fine structure in the hydrogen
kinetic energy distribution. While caging is negligible for the smallest clusters,
it becomes more efficient upon increasing the cluster size,          
and for twelve solvent atoms the cage effect
is already very strong. Finally, it is shown that while in the ground state the
hydrogen atom points essentially towards the rare gas cluster, in excited librational
states hydrogen is directed mostly away from argon atoms. As a consequence, 
caging of the photodissociating
hydrogen atom in the case of a surface solvated HCl molecule
can be efficiently "turned off" by librational preexcitation.