Resonant two-color detachment of ${\mathrm{H}}^{\mathrm{-}}$ with excitation of H(n=2)

The cross sections for resonant two-color, two-photon detachment of ${\mathrm{H}}^{\mathrm{-}}$ with excitation of the degenerate H(2s) and H(2p) levels are calculated within a semiempirical adiabatic hyperspherical representation. The first photon, with energy ${\mathrm{\omega }}_1$=0.4017 a.u., is resonant with the well-known Feshback ${}_{}{}^1{}_{}{}^{}$${\mathit{P}}^{\mathit{o}}$ resonance below the H(n=2) threshold. The second photon, with energy ${\mathrm{\omega }}_2$≥0.126 05 a.u., scans the energy region above the H(n=2) threshold over which long-range dipole-field-induced cross-section oscillations are predicted to occur. Such Gailitis-Damburg oscillations have not yet been observed experimentally. Results for various pairs of light polarization for the two photons are presented. Our resonant two-color, two-photon detachment cross sections are 8–9 orders of magnitude greater than the corresponding nonresonant, single-color, two-photon detachment cross sections obtained by Liu, Du, and Starace [Phys. Rev. A 43, 5891 (1991)]. Unmistakable evidence of long-range dipole-field effects is presented over the 5-meV energy range above the H(n=2) threshold. Furthermore, the differential cross sections for right- and left-circularly polarized, copropagating photons and especially the circular dichroism differential cross sections are shown to have nearly a full cycle of a greatly enhanced dipole-field-induced oscillation extending over the region from threshold to ≊34 meV above.