Theoretical calculation of two-photon absorption cross sections in atomic oxygen

Abstract

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{'}}$${\ensuremath{\sigma}}_{0}^{(2)}$(J'\ensuremath{\leftarrow}J) of (1.319\ifmmode\pm\else\textpm\fi{}0.2)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}35}$ ${\mathrm{cm}}^{4}$ has been obtained, which is in excellent agreement with the experimental value for the quantity ${\mathcal{J}}_{J\mathcal{'}}$${\ensuremath{\sigma}}_{0}^{(2)}$(J'\ensuremath{\leftarrow}2)${G}^{(2)}$ =(2.66\ifmmode\pm\else\textpm\fi{}0.80)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}35}$ ${\mathrm{cm}}^{4}$, given in the companion paper, if the photon statistical factor, ${G}^{(2)}$, is evaluated in the chaotic field limit (${G}^{(2)}$=2).