Two-photon absorption cross sections for transitions from the O${(\mathrm{}}^3$P) ground electronic state to the 3p ${}^3$P, 4p ${}^3$P, and the autoionizing ${\mathrm{O}}^{+}$(${\mathrm{}}^2$D)3p’ and ${\mathrm{O}}^{+}$(${\mathrm{}}^2$P)3p’’ states have been calculated by explicit evaluation of the perturbation-theory summation using matrix elements calculated from configuration-interaction wave functions and sum rules to correct for truncation. The role of different contributions in the summation has been analyzed. For the 3p ${}^3$P state, a cross section of ${\mathcal{J}}_{J\mathcal{’}}$${\sigma }_0^{\mathrm{}\left(2\right)\mathrm{}}$(J’←J) of (1.319±0.2)×${10}^{\mathrm{-}35}$ ${\mathrm{cm}}^4$ has been obtained, which is in excellent agreement with the experimental value for the quantity ${\mathcal{J}}_{J\mathcal{’}}$${\sigma }_0^{\mathrm{}\left(2\right)\mathrm{}}$(J’←2)$G^{\mathrm{}\left(2\right)\mathrm{}}$ =(2.66±0.80)×${10}^{\mathrm{-}35}$ ${\mathrm{cm}}^4$, given in the companion paper, if the photon statistical factor, $G^{\mathrm{}\left(2\right)\mathrm{}}$, is evaluated in the chaotic field limit ($G^{\mathrm{}\left(2\right)\mathrm{}}$=2).

• Received 3 February 1986

DOI:https://doi.org/10.1103/PhysRevA.34.199