Using synchrotron-radiation-based angle-resolved photoelectron spectroscopy, the relative partial photoionization cross sections for the production of the ${}_{}{}^4{}_{}{}^{}$${\mathit{S}}^{\mathit{o}}$ and ${}_{}{}^2{}_{}{}^{}$${\mathit{D}}^{\mathit{o}}$ ionic states in atomic oxygen, as well as the corresponding asymmetry parameters, are measured from threshold at 13.62 to about 30 eV. The cross sections are placed on an absolute scale using previous data obtained with an electron spectroscopy modulation method. Attention is focused on the numerous autoionization resonances below the 2${\mathit{p}}^{\mathrm{-}1}$ ${}_{}{}^2{}_{}{}^{}$${\mathit{D}}^{\mathit{o}}$, 2${\mathit{p}}^{\mathrm{-}1}$ ${}_{}{}^2{}_{}{}^{}$${\mathit{P}}^{\mathit{o}}$, and 2${\mathit{s}}^{\mathrm{-}1}$ ${}_{}{}^4{}_{}{}^{}$${\mathit{P}}^{\mathit{e}}$ limits. The behavior of the asymmetry parameters across these resonances is observed for the first time. The 2s2${\mathit{p}}^4$${(}^4$${\mathit{P}}^{\mathit{e}}$)3p${(}^3$${\mathit{S}}^{\mathit{o}}$${,}^3$${\mathit{P}}^{\mathit{o}}$${,}^3$${\mathit{D}}^{\mathit{o}}$) resonances are fitted by a Fano-type profile to obtain accurate values for the position, width, and q parameter.

• Received 11 January 1991

DOI:https://doi.org/10.1103/PhysRevA.43.5997