Some ab initio valence bond studies of the H5 anion

The results of some ab initio valence bond calculations with 1s basis sets are reported for the anion H⁻₅ as H₂H⁻H₂. Both single-zeta and double-zeta calculations have been performed, with attention given primarily to the results of the single-zeta calculations. For the latter calculations, it is shown that both polarization of the H₂ bonds, and charge transfer from the H⁻ to the H₂ contribute to the binding of the linear anion. In order that bending may occur, it is necessary in these calculations to include a 1s midbond function, whose exponent is the same as that for the 1s atomic orbital of the H⁻. The midbond function is located midway between the hydrogen atoms that are adjacent to the H⁻. With a single-zeta basis, the calculated bond angle is 165°.