Alkali atoms attached to He-3 nanodroplets

We have experimentally studied the electronic 3p <- 3s excitation of Na atoms attached to He-3 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 He-4 droplets, we conclude that sodium atoms reside in a dimple on the droplet surface and that supefluid-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, He-3 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.