Density of Superfluid Helium Droplets

TL;DR

This paper reports experimental measurements of large superfluid helium droplets' cross sections and atom counts, aligning well with density functional predictions, and derives surface thickness estimates from the data.

Contribution

It provides experimental validation of density functional calculations for superfluid helium droplets and introduces a simple model to estimate surface thickness from scattering data.

Findings

Measured cross sections agree with density functional predictions.

Estimated surface thickness of droplets is about 6-8 Å.

Validated a simple density profile model for helium droplets.

Abstract

The classical integral cross sections of large superfluid 4He_N droplets and the number of atoms in the droplets (N=10^3-10^4) have been measured in molecular beam scattering experiments. These measurements are found to be in good agreement with the cross sections predicted from density functional calculations of the radial density distributions with a 10-90 % surface thickness of 5.7\AA. By using a simple model for the density profile of the droplets a thickness of about 6-8\AA is extracted directly from the data.