The twohyphen;photon first ionization cross section was computed for H2O in the vertical transition approximation. A Stieltjes imaging technique was used to obtain from the results of aL2basis set calculation, the twohyphen;photon oscillator strength density in the continuum. The calculations were performed in the independent particle statichyphen;exchange approximation for the final states. The groundhyphen;intermediate state transition matrix elements and excitation energies were computed by adopting the single channel statichyphen;exchange approximation or the multichannel random phase approximation; in the last case the intermediatehyphen;final state transition matrix elements were obtained by the equation of motion method. The calculated cross sections refer to the case of single beam of linearly or circularly polarized photons.
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