The structure and energetics of ${}^3$He and ${}^4$He nanodroplets doped with alkaline earth atoms

Abstract

We present systematic results, based on density functional calculations, for the structure and energetics of ${}^3$He and ${}^4$He nanodroplets doped with alkaline earth atoms. We predict that alkaline earth atoms from Mg to Ba go to the center of ${}^3$He drops, whereas Ca, Sr, and Ba reside in a deep dimple at the surface of ${}^4$He drops, and Mg is at their center. For Ca and Sr, the structure of the dimples is shown to be very sensitive to the He-alkaline earth pair potentials used in the calculations. The $5s5p\leftarrow 5s^2$ transition of strontium atoms attached to helium nanodroplets of either isotope has been probed in absorption experiments. The spectra show that strontium is solvated inside ${}^3$He nanodroplets, supporting the calculations. In the light of our findings, we emphasize the relevance of the heavier alkaline earth atoms for analyzing mixed ${}^3$He-${}^4$He nanodroplets, and in particular, we suggest their use to experimentally probe the ${}^3$He-${}^4$He interface.

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