Asymptotic and interpolation series for the Coulomb three-body systems with unit charges

Accurate mass-interpolation and mass-asymptotic formulas are derived for one- and two-center three-body ions with unit charges. The derived formulas are applied to predict accurate numerical values of the total energies of the ground (bound) $1^{1}S(L=0)-$states in one-center atomic ions $X^{+} e^{-} e^{-}$andanalogousground(bound)$1 s \sigma-$states in the two-center, quasi-adiabatic (or quasi-molecular) $X^{+}{X}^{+}{e}^{-}$ ions. We also discuss a few problems which currently remain unsolved for the $Q^{-1}$ expansions constructed for the ground (bound) states in few-electron atoms and ions.