Molecular Photodetachment Spectrometry. II. The Electron Affinity ofO2and the Structure ofO2−

A beam of ${\mathrm{O}}_2^{-}$ ions, extracted from a glow discharge in ${\mathrm{N}}_2$O, is crossed with the linearly polarized intracavity photon beam of an argon-ion laser (4880 Å). Electrons photodetached at right angles to the crossed beams are energy filtered by a hemispherical analyzer. The electron energy spectra are characteristic of photodetachment from the $v^{\prime }=0\mathrm{}$ state of ${\mathrm{O}}_2^{-}$ to the $X{}_{}{}^3{}_{}{}^{}\Sigma _g^{-}{}_{}{}^{}$ and $a{}_{}{}^1{}_{}{}^{}\Delta _g^{}{}_{}{}^{}$ states of ${\mathrm{O}}_2$. Vibrational state analysis is facilitated by the use of isotopes. The electron affinity obtained is 0.440 ± 0.008 eV. Additionally, we have measured the relative transition probabilities as a function of final vibrational state and the angular distributions of the outgoing electrons. The relative intensities, corrected by the angular distributions, determine through Franck-Condon-factor analysis the internuclear distance for the negative ion. We find ${\mathcal{r}}_e^{\prime \prime }=1.341\mathrm{}\pm 0.010$ Å and therefore $B_e^{\prime \prime }=1.17\mathrm{}\pm 0.02$ ${\mathrm{cm}}^{-1\mathrm{}}$.