Multiphoton-detachment cross sections forH−

Abstract

Perturbation theory is applied to the evaluation of the multiphoton-detachment cross sections of ${\mathrm{H}}^{\mathrm{-}}$ in a number of approximations. The zero-range plane-wave approximation is the simplest, as its effective dipole matrix element is reducible to a recursive differentiation, and it is applied to the one- to seven-photon-detachment processes. Improvements on this are made in the bound state by means of a short-range potential model and a dynamic screening representation, and in the continuum wave functions with the use of the best previously calculated e-H(1s) singlet scattering phase shifts. The dynamic screening parameters are adjusted to give a good fit of the resulting one-photon cross section to its correct well-known value, and the accurate phase shifts effectively include all the important correlation effects in the free-free amplitudes. These improved wave functions are used for the evaluation of the two- and three-photon generalized detachment cross sections by explicitly carrying out all intermediate state sums. Our best σ${\mathrm{^}}_2$ and σ${\mathrm{^}}_3$ are estimated to be accurate to order 5%. The present theoretical results are compared with other calculations and recent measurements, revealing areas of agreement as well as certain discrepancies.