MULTIPHOTON DETACHMENT OF H- .2. INTENSITY-DEPENDENT PHOTODETACHMENT RATES AND THRESHOLD BEHAVIOR - COMPLEX-SCALING GENERALIZED PSEUDOSPECTRAL METHOD

We extend our previous perturbative study of the multiphoton detachmen t of H- [Phys. Rev. A 48, 4654 (1993)] to stronger fields by consideri ng the intensity-dependent photodetachment rates and threshold behavio r. An accurate one-electron model potential, which reproduces exactly the known H- binding energy and the low-energy e-H(1s) elastic-scatter ing phase shifts, is employed. A computational technique, the complex- scaling generalized pseudospectral method, is developed for accurate a nd efficient treatment of the time-independent non-Hermitian Floquet H amiltonian H(F). The method is simple to implement, does not require t he computation of potential matrix elements, and is computationally mo re efficient than the traditional basis-set-expansion-variational meth od. We present detailed nonperturbative results of the intensity- and frequency-dependent complex quasienergies (E(R), - GAMMA/2), the compl ex eigenvalues of H(F), providing directly the ac Stark shifts and mul tiphoton detachment rates of H-. The laser intensity considered ranges from 1 to 40 GW/cm2 and the laser frequency covers 0.20-0.42 eV (in t he c.m. frame). Finally we perform a simulation of intensity-averaged multiphoton detachment rates by considering the experimental condition s of the laser and H- beams. The results (without any free parameters) are in good agreement with experimental data, both in absolute magnit ude and in the threshold behavior.