Quantum over-barrier reflection effects manifested in photodetachment cross sections

The photodetachment of H- near a potential barrier is studied. A new formula is presented for the cross sections induced by a barrier. The new formula describes two quantum effects near the barrier tops. For energies near and above the barrier tops, the quantum over-barrier reflection effects are included and the induced oscillations in the cross sections are still prominent; for energies near and below the barrier tops, the quantum tunnelling across barriers is taken into account and consequently the oscillations are weakened. For energies far away from the barrier tops, the new formula agrees with the standard closed-orbit theory. We demonstrate that a potential barrier of various width and location can be realized by placing a negative ion near a metal surface and applying an electric field pointing to the surface. The width and location of the barrier can be systematically changed by varying the electric field strength and the distance between the negative ion and the surface. Results are also presented for estimating the sizes and locations of the aforementioned quantum effects in the cross sections.