The thesis is organized as follows: in the first chapter we provide a short description
of the scenario which frames our work. Some significant experiments
are presented, together with the questions raised by them, the theoretical investigations
they stimulated, and the open issues. The second chapter describes the
reptation quantum Monte Carlo method and its theoretical foundations. Technical
aspects (the choice of the trial functions, the procedure to calculate the cluster
rotational energies) are discussed in third chapter. We also report some studies
on the reptation algorithm. In the fourth chapter we apply RQMC for the interpretation
of the infrared spectra of CO@HeN [5]. The fifth chapter addresses the
problem of the evolution of the rotational dinamics of He solvated rotors toward
the nanodroplet regime; two paradigmatic cases, OCS@HeN and HCN@HeN , are
studied. Our conclusions are drawn in the last chapter
