Quantum hydrodynamic model for the enhanced moments of inertia of molecules in helium nanodroplets: Application to SF6

The increase in moment of inertia of SF$_6$ in helium nanodroplets iscalculated using the quantum hydrodynamic approach. This required an extensionof the numerical solution to the hydrodynamic equation to three explicitdimensions. Based upon an expansion of the density in terms of the lowest fourOctahedral spherical harmonics, the predicted increase in moment of inertia is$170 {\rm u \AA^2}$, compared to an experimentally determined value of $310(10){\rm u \AA^2}$, i.e., 55% of the observed value. The difference is likely in atleast part due to lack of convergence with respect to the angular expansion,but at present we do not have access to the full densities from which a higherorder expansion can be determined. The present results contradict those of Kwonet al., J. Chem. Phys. {\bf 113}, 6469 (2000), who predicted that thehydrodynamic theory predicted less than 10% of the observed increase in momentof inertia.Comment: 10 pages, including 1 figur