  The rotational dynamics of CO single molecules solvated in small He clusters
(CO@He_N) has been studied using Reptation Quantum Monte Carlo for cluster
sizes up to N=30. Our results are in good agreement with the roto-vibrational
features of the infrared spectrum recently determined for this system, and
provide a deep insight into the relation between the structure of the cluster
and its dynamics. Simulations for large N also provide a prediction of the
effective moment of inertia of CO in the He nano-droplet regime, which has not
been measured so far.
