The theory of configuration interaction in molecules is extended to permit the simultaneous treatment of doubly excited electronic states and vibrationally excited Rydberg states which can decay by autoionization and predissociation. The method is applied to dissociative recombination and compared with the corresponding multichannel quantum-defect theory. Calculations using both techniques are reported for collisions of electrons of energy below 0.5 eV with ${\mathrm{H}}_2^{+}$ ions in the lowest three vibrational states. The Rydberg states lead to narrow structures in the cross sections, mostly in the form of dips. The cross section and recombination rate for ground-state ions are anomalously low, being smaller than those for $v=1\mathrm{} \mathrm{and} 2$ by a factor of ∼6.

• Received 22 September 1982

DOI:https://doi.org/10.1103/PhysRevA.28.682