Simple discretization method for autoionization widths. III. Molecules

We apply a new method to calculate widths of two-electron Feshbach resonances, which was described in detail and applied to atomic systems in preceding articles (this issue), to molecular and quasimolecular autoionizing states. For simplicity in the programming effort, we restrict our calculations to the small-R region where one-centered expansions are sufficiently accurate to describe the wave functions. As test cases, positions and widths for the H₂, He₂{}²⁺$, ${HeH}⁺$, and ${LiHe}³⁺$ resonances of lowest energy are computed for R0.6 a.u. The advantage of using block-diagonalization techniques to define diabatic resonant states instead of generalizing the Feshbach formalism is pointed out.