The second (unphysical) critical charge in the 3-body quantum Coulomb system of a nucleus of positive charge Z and mass m p , and two electrons, predicted by F Stillinger has been calculated to be equal to Z ∞ B = 0.904854 and Z mp B = 0.905138 for infinite and finite (proton) mass m p , respectively. It is shown that in both cases, the ground state energy E(Z) (analytically continued beyond the first critical charge Z c , for which the ionization energy vanishes, to ReZ < Z c ) has a square-root branch point with exponent 3/2 at Z = Z B in the complex Z-plane. Based on analytic continuation, the second, excited, spin-singlet bound state of negative hydrogen ion H − is predicted to be at -0.51554 a.u. (-0.51531 a.u. for the finite proton mass m p ). The first critical charge Z c is found accurately for a finite proton mass m p in the Lagrange mesh method, Z mp c = 0.911 069 724 655.