The Schrödinger equation for the ion is solved in prolate spheroidal coordinates using the pseudospectral method. The Stark resonance parameters for the two lowest states of the ion have been determined by adding a complex absorbing potential to the Hamiltonian. The localized electron densities for both (lower and upper) states are obtained to provide explanations for structures seen in the ionization rate as a function of internuclear separation. The Riss–Meyer iterative and Padé extrapolation methods are applied to obtain highly accurate values for the resonance parameters, which are compared to previous results.