The doubly excited autoionizing states of H2

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Abstract
Ab initio potential curves have been determined for 24 doubly excited autoionizing states of H2 having primarily the lowest 2Σ+u and 2Πu states of H+2 as the core orbital. Fourteen of these states have not appeared previously in the literature. The configuration interaction wave functions are constructed with a Feshbach projection operator formalism. The accuracy of the calculations is assessed by comparison with calculations in the same bases on the lower bound states of H2. The potential curves for the doubly excited states fall into three distinct groups with an energy ordering related to the Hartree energy of the most important configuration of each state. The relative energies of several doubly excited states and the corresponding singly excited bound states of H2 are compared. The grouping of doubly excited states is in good agreement with the electron impact results of Kollman. Both the lowest two states of Q1 1Σ+u symmetry and a Q2 1Σ+u state with thresholds of 25.5, 27.8, and 33.3 eV, respectively, are important in the interpretation of dissociative photoionization and electron impact experiments. A Q2 1Σ+g state with a threshold at 30.2 eV will contribute to the fast H atoms seen in several electron impact experiments.