Variational calculation of some S-states of Coulomb three-body systems

A generalized Hylleraas-type basis set with three nonlinear parameters is p roposed to study three-body systems interacting via coulomb forces within t he framework of non-relativistic quantum mechanics. This basis set improves the rate of convergence with respect to previous ones, specially for nonsy mmetric systems and excited states of two electron atoms: Accurate binding energies and other properties for S-states of helium-like ions, muonic mole cules and the positronium negative ion are reported.