  Accurate computer simulations of the rotational dynamics of linear molecules
solvated in He clusters indicate that the large-size (nano-droplet) regime is
attained quickly for light rotors (HCN, CO) and slowly for heavy ones (OCS,
N$_2$O, CO$_2$), thus challenging previously reported results. Those results
spurred the view that the different behavior of light rotors with respect to
heavy ones - including a smaller reduction of inertia upon solvation of the
former - would result from the lack of adiabatic following of the He density
upon molecular rotation. We have performed computer experiments in which the
rotational dynamics of OCS and HCN molecules was simulated using a fictitious
inertia appropriate to the other molecule. These experiments indicate that the
approach to the nano-droplet regime, as well as the reduction of the molecular
inertia upon solvation, is determined by the anistropy of the potential, more
than by the molecular weight. Our findings are in agreement with recent
infrared and/or microwave experimental data which, however, are not yet totally
conclusive by themselves.
