M. Pont et R. Shakeshaft, ABSOLUTE CROSS-SECTIONS FOR DOUBLE PHOTOIONIZATION OF HELIUM AT ENERGIES FROM 0 TO 80 EV ABOVE-THRESHOLD, Journal of physics. B, Atomic molecular and optical physics, 28(18), 1995, pp. 571-577
We have performed, using an ab initio basis-set method, calculations o
f the absolute cross section for double photoionization of helium for
energies from 2 to 80 eV above threshold, and we have extended the res
ults down to 0 eV through spline interpolation. Our results are consis
tent with the Wannier threshold law, and agree well with the near-thre
shold mesurements. At higher energies (20 eV or so above threshold) si
gnificant discrepancies with experiment are evident. We find a simple
relation between the integrated cross section for double photoionizati
on and the singly differential cross section at the midpoint of the en
ergy distribution.