Multiphoton detachment ofH−. II. Intensity-dependent photodetachment rates and threshold behavior—complex-scaling generalized pseudospectral method

We extend our previous perturbative study of the multiphoton detachment of ${\mathrm{H}}^{\mathrm{\ensuremath{-}}}$ [Phys. Rev. A 48, 4654 (1993)] to stronger fields by considering the intensity-dependent photodetachment rates and threshold behavior. An accurate one-electron model potential, which reproduces exactly the known ${\mathrm{H}}^{\mathrm{\ensuremath{-}}}$ binding energy and the low-energy e-H(1s) elastic-scattering phase shifts, is employed. A computational technique, the complex-scaling generalized pseudospectral method, is developed for accurate and efficient treatment of the time-independent non-Hermitian Floquet Hamiltonian H${\mathrm{^}}_{\mathit{F}}$. The method is simple to implement, does not require the computation of potential matrix elements, and is computationally more efficient than the traditional basis-set-expansion--variational method. We present detailed nonperturbative results of the intensity- and frequency-dependent complex quasienergies (${\mathit{E}}_{\mathit{R}}$,-\ensuremath{\Gamma}/2), the complex eigenvalues of H${\mathrm{^}}_{\mathit{F}}$, providing directly the ac Stark shifts and multiphoton detachment rates of ${\mathrm{H}}^{\mathrm{\ensuremath{-}}}$. The laser intensity considered ranges from 1 to 40 GW/${\mathrm{cm}}^{2}$ and the laser frequency covers 0.20--0.42 eV (in the c.m. frame). Finally we perform a simulation of intensity-averaged multiphoton detachment rates by considering the experimental conditions of the laser and ${\mathrm{H}}^{\mathrm{\ensuremath{-}}}$ beams. The results (without any free parameters) are in good agreement with experimental data, both in absolute magnitude and in the threshold behavior.