Two- and three-photon detachment ofH−by a weak field

Abstract
We describe a method for calculating rates for multiphoton detachment or ionization of a two-electron system by a perturbative field. We have applied the method to H, and we present estimates of two- and three-photon detachment rates. In particular, we explore the 1 Se and 1 De Feshbach resonances below the n=2 and n=3 excitation thresholds of H; these resonances lie in the ‘‘excess-photon detachment’’ regime, where one photon is already sufficient to detach the electron.