Two-photon detachment of electrons from halogen negative ions

Absolute two-photon detachment cross sections and photoelectron angular
distribution are calculated for halogen negative ions within lowest-order
perturbation theory. The outer $np$ ground-state wavefunctions are
determined using the Dyson equation method. The {\em ab initio} correlation
potential is scaled by introduction of a free parameter. We choose it to
ensure that the $np$ wavefunctions have a proper asymptotic behavior
$P(r)\propto \exp (-\kappa r)$, corresponding to correct
(experimental) binding energies $E_b=\hbar ^2\kappa ^2/2m$. The latter
is crucial for obtaining correct absolute values of the multiphoton
cross sections (Gribakin and Kuchiev 1997 {\em Phys. Rev. A} {\bf 55} 3760).
Comparisons with previous calculations and experimental data are performed.