The binding of alkali atoms to the surfaces of liquid helium and hydrogen

Alkali atoms have been shown previously to have only unstable binding states inside liquid⁴He. We calculate the equilibrium configurations and binding energies of single alkali atoms near the liquid-vapor interface of⁴He and³He. A simple interface model is used to predict the surface deformation due to the presence of the atoms. A more realistic density functional model yields somewhat higher energies in the case of⁴He. For all alkali atoms, we find the surface binding energies to be around 10 to 20 K. A similar analysis with atom-H₂ interactions finds that alkali atoms tend to submerge into liquid H₂, with the exception of Li.