A superfluid hydrodynamic model for the enhanced moments of inertia of molecules in liquid 4He

TL;DR

This paper introduces a superfluid hydrodynamic model that explains the increased moments of inertia of molecules rotating in liquid helium-4, aligning well with experimental data for some molecules but overestimating for others due to approximation limits.

Contribution

The paper develops a hydrodynamic model based on the adiabatic following approximation to explain molecular moments of inertia in superfluid helium-4, providing improved understanding over previous models.

Findings

Model agrees with observed $mbda I$ increases for several molecules

Overestimates $mbda I$ for HCN and HCCH, indicating approximation breakdown

Supports the superfluid flow explanation for inertia enhancement

Abstract

We present a superfluid hydrodynamic model for the increase in moment of inertia, $\Delta I$, of molecules rotating in liquid $^4$He. The static inhomogeneous He density around each molecule (calculated using the Orsay-Paris liquid $^4$He 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 for several molecules [ OCS, (HCN)$_2$, HCCCN, and HCCCH$_3$ ]. For HCN and HCCH, our model substantially overestimates $\Delta I$. This is likely to result from a (partial) breakdown of the adiabatic following approximation.