Resonant-Like~Enhancement~of~the High-Energy Plateau in ATD

We calculate the intensity variation of above-threshold detachment (ATD) rates for H$^{-}$ and F$^{-}$ in the high-energy plateau region, by solving the time-dependent Schr\"odinger equation within the Sturmian-Floquet approach [1]. We find pronounced enhancement of the ATD spectra as the laser-field intensity induces ATD channel closings. We confirm previous results on negative ions with an active s-electron [2], and extend them to the case of p-symmetry of the initial state. Depending on the symmetry of the initial state, we show that the enhancement is most pronounced for even- or odd-channel closures. Similar resonant-like enhancements have been observed experimentally in above-threshold ionization spectra for rare gases [3], calculations for which are in progress. [1] R. M. Potvliege, {\it Comp. Phys. Comm.} {\bf 114}, 42 (1998); [2] B. Borca {\it et al.}, {\it Phys. Rev. Lett.} {\bf 88}, 193001 (2002); [3] See, e.g., F. Grasbon {\it et al.}, {\it Phys. Rev. Lett.} {\bf 91}, 173003 (2003).