Superfluid hydrodynamic model for the enhanced moments of inertia of molecules in liquid He-4

We present a superfluid hydrodynamic model for the increase in moment of in ertia, Delta I, of molecules rotating in liquid He-4. The static inhomogene ous He density around each molecule (calculated using the Orsay-Paris liqui d He-4 density functional) is assumed to adiabatically follow the rotation of the molecule. We find that the Delta I values created by the viscousless and irrotational flow are in good agreement with the observed increases fo r several molecules [OCS, (HCN)(2), HCCCN, and HCCCH3]. For HCN and HCCH, o ur model substantially overestimates al. This is likely to result from a (p artial) breakdown of the adiabatic following approximation.