Alkali Atoms Attached to $^3$He Nanodroplets

TL;DR

This study investigates the electronic excitation of sodium atoms attached to helium-3 nanodroplets using spectroscopy and density functional calculations, revealing their surface location and negligible superfluid effects.

Contribution

It provides experimental and theoretical evidence that sodium atoms reside on the surface of helium-3 droplets, with calculated spectral shifts matching experimental data.

Findings

Na atoms are located on the droplet surface.

Spectral shifts are consistent with surface attachment.

Superfluid effects are negligible for Na on $^3$He droplets.

Abstract

We have experimentally studied the electronic $3p-> 3s$ excitation of Na atoms attached to $^3$He droplets by means of laser-induced fluorescence as well as beam depletion spectroscopy. From the similarities of the spectra (width/shift of absorption lines) with these of Na on $^4$He droplets, we conclude that sodium atoms reside in a ``dimple'' on the droplet surface and that superfluid-related effects are negligible. The experimental results are supported by Density Functional calculations at zero temperature, which confirm the surface location of Na, K and Rb atoms on $^3$He droplets. In the case of Na, the calculated shift of the excitation spectra for the two isotopes is in good agreement with the experimental data.