The Rotational Structure of Molecules In the Quantum He4 and He3 Liquids

TL;DR

This paper explains the differing rotational structures of molecules in He4 and He3 liquids by analyzing their excitation spectra, revealing that particle-hole and phonon excitations cause distinct broadening effects.

Contribution

It provides a spectral density-based explanation for the contrasting rotational behaviors of molecules in He4 and He3 liquids, linking microscopic excitations to observed phenomena.

Findings

Particle-hole excitations cause broad rotational levels in He3.

Low phonon density results in narrow rotational levels in He4.

Spectral density differences explain the observed rotational structure distinctions.

Abstract

It is shown that the drastic distinction in the rotational structure of molecules in the He4 and He3 liquids observed in [1] is due to the difference in the spectral density of excitations regardless of the hydrodynamic properties. The large width of rotational levels in the He3 is determined by particle-hole excitations whereas the small density of phonon excitations results only in the small broadening of levels in the He4.