Quasiclassical double photoionization from the 21,3S states of helium including shakeoff

We account for the different symmetries of the 2 1,3S helium excited states in a quasiclassical description of the knockout mechanism augmented by a quantum shake-off contribution. We are thus able to formulate the separate contributions of the knockout and shake-off mechanisms for double photoionization for any excess energy from the 2 1,3S states. Photoionization ratios and single-differential cross sections calculated for the 2 1,3S excited states of helium are found to be in very good agreement with recent theoretical results. 1