Structure of Helium–Alkali Pentamers

Abstract

We report a diffusion Monte Carlo study of helium–alkali pentamers $$^4$$ He $$_4$$ A, $$^3$$ He $${}^4$$ He $$_3$$ A and $$^3$$ He $$_2{}^4$$ He $$_2$$ A, where A is one of the alkali atoms $$^{6,7}$$ Li, $$^{23}$$ Na, $$^{39,40,41}$$ K, $$^{85,87}$$ Rb or $$^{133}$$ Cs. Exact ground state properties, binding energies and structure, were extracted for selected interaction models. Studied five-body systems show wide spatial extent, which is one of the halo state characteristics. For that reason they are expected to be very close to the halo limit. Calculated pair distributions and density profiles enabled insight into atom arrangements when adding different masses of alkali metals to the halo and quai-halo helium tetramers. Four helium atoms mainly group on one side of an alkali metal, surrounding it extremely rarely and only when $$^3$$ He is present. Only occasionally $$^3$$ He $$_2{}^4$$ He $$_2$$ surround the smallest alkali—Li, less frequently Na, almost never bigger A.