A new method for computing properites of negative ion resonances with application to 2Σ+u states of H−2

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Abstract
A new method for computing properties of negative ion resonances is reported. The first step is to carry out a CI calculation of the lowest 15 or so states of proper symmetry of the negative ion system. A Feshbach projection‐operator technique is then used to project out the various resonances from the CI states. The projection is based on the assumption that resonances have small expectation values for the one‐electron operator z2 and continuum states have large values. The energies, energy widths, and lifetimes of the resonances are then straightforward to calculate. The method has been applied to the 2Σ+u states of H−2. Two resonances reported here have been seen by other workers, but a third, which lies 5.8 eV above the v=0 level of H2, has not been identified before. The implication of this resonance for electron‐hydrogen scattering experiments is discussed.