Continuum electronic wavefunctions in the static-exchange approximation for resonant processes in diatomic molecules. I. Widths for electron capture in the CH⁺closed-shell molecular ion

The wavefunction of a low-energy unbound electron in the field of a closed-shell diatomic molecular ion is calculated using a single-centre expansion in the static-exchange approximation. The evaluation is reported of the electronic capture width necessary for the calculation of the dissociative-recombination rate of the CH + ion in its ground state, with a two-centre molecular integral program. The agreement between calculated values for a very low energy (0.01 eV) and extrapolated values from Rydberg states, found both for the quantum defect and the electronic-capture width, establishes the reliability of the direct calculation.