Rotational level structure of SF6-doped 4HeN clusters

We present diffusion Monte Carlo calculations of low-lying rotational states of (HeNSF6)-He-4 which confirm recent experiments suggesting that dopant molecules trapped inside He-4 clusters behave as free rotors. Analysis of the rotational wave functions leads to a clear physical explanation for this effect based on angular momentum coupling arguments; a fraction of the helium density is found to follow the rotation of the SF6 molecule adiabatically. This leads to a free-rotor spectrum and to a reduction in the effective rotational constant that is in excellent quantitative agreement with experiment.