The Structure and Energetics of ³He and ⁴He Nanodroplets Doped with Alkaline Earth Atoms

Abstract

We present systematic results, based on density functional calculations, for the structure and energetics of 3He and 4He nanodroplets doped with alkaline earth atoms. We predict that alkaline earth atoms from Mg to Ba go to the center of 3He drops, whereas Ca, Sr, and Ba reside in a deep dimple at the surface of 4He 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 <-- 5s2 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 3He nanodroplets, supporting the calculations. In the light of our findings, we emphasize the relevance of the heavier alkaline earth atoms for analyzing mixed 3He-4He nanodroplets, and in particular, we suggest their use to experimentally probe the 3He-4He interface.

Simulations of the dissociation of small helium clusters with ab initio molecular dynamics in electronically excited states

“…30 The initial conditions for solving the equations correspond to those at the time of ionization, i.e., the equilibrium configuration of the neutral Ba@4He 1000 complex. DF calculations find this configuration to have the Ba atom residing in a dimple at the surface of the droplet, 31 in agreement with experiments. 32,33 Snapshots of the dynamical evolution of the Ba + @ 4 He 1000 system are presented in Fig.…”

Spectroscopy of barium atoms in liquid and solid helium matrices

“…Recent advances in the development of ab initio Ba-He interaction potentials in the ground and excited states [25][26][27] open possibilities that did not exist in the early 1990s, for the quantitative modeling of superfluid and solid quantum matrix-isolated barium atoms. Such model calculations have been recently performed for the Ba atoms on helium droplets [28]. The extensive spectroscopic data provided here will prove useful for testing the modeling of the Ba-He interaction in bulk matrices.…”

Ca impurity in small mixed H4e–H3e clusters

“…This scenario has been confirmed by density functional (DF) calculations [12,13]. Heavy alkaline-earth atoms thus may offer a unique opportunity to study the interface of isotopically mixed helium clusters [14].…”

“…7, which is absent in the other clusters. Eventually, when the number of 3 He atoms increases, the center-of-masses of the helium moiety and the impurity nearly coincide [14].…”