Bw. Yang et al., DESCRIPTION OF A 2-ELECTRON ATOM OR ION IN AN AC FIELD USING INTERPARTICLE COORDINATES, WITH AN APPLICATION TO H-, Physical review. A, 56(6), 1997, pp. 4946-4959
We provide a general formulation of the energy eigenvalue problem for
a two-electron atomic system interacting with a monochromatic radiatio
n field using interparticle coordinates to describe the internal motio
n; electron correlation is fully incorporated. No restriction is place
d on the total orbital angular momentum of the system. We have applied
this formulation using the perimetric combination of interparticle co
ordinates to the calculation of accurate second- and fourth-order ac s
hifts and widths of the negative hydrogen ion. In addition, we have ob
tained estimates of the ac shifts and widths in the nonperturbative re
gime, using a three-level model Hamiltonian constructed from the zerot
h-, first-, and second-order perturbed wave functions. We have used th
is model to investigate the intensity dependence of absorption profile
s in the autoionizing resonance region below the two-electron escape t
hreshold. We have also used the model to estimate the intensity for on
set of stabilization (against ionization) at frequencies above the thr
eshold for two-electron escape; the onset intensity increases as the t
hird power of the frequency, in accord with earlier results for atomic
hydrogen. [S1050-2947(97)09311-6].