Extensive eigenchannelR-matrix study of theH−photodetachment spectrum

We combine an eigenchannel R-matrix calculation with an analytic description of electron motion in a dipole field to predict photodetachment cross sections of the hydrogen negative ion, including resonant structures up to the n=4 hydrogenic threshold. Partial cross sections for the production of hydrogen-atom fragments in states with specific principal quantum numbers n are also presented for comparison with a recent experiment. An analysis of the delay-time matrix indicates that the autodetaching Feshbach resonances decay primarily into the nearest energetically accessible continuum channel, an observation which is not at all apparent from the calculated and observed partial cross sections, but has been anticipated in previous theoretical work. We find, for instance, that the ${}_{\mathit{n}=4\mathrm{}}{}^{}{}_{}{}^{}\mathit{v}$=0${\mathrm{\}}}_{\mathit{m}=4\mathrm{}}^{\mathit{A}=+}$ resonant state below the H(n=4) threshold decays 73% of the time to the ${}_3{}^{}{}_{}{}^{}\mathrm{\}}_{}^{+}{}_{}{}^{}$ photodetachment channel.