Fine Structure ofO2+Measured by Electron Time-of-Flight Spectroscopy

A high-resolution electron time-of-flight spectrometer has been used in a transmission experiment to study resonances in $e$-${\mathrm{O}}_2$ scattering corresponding to vibrationally excited levels of the ${\mathrm{O}}_2^{-}$ ${}_{}{}^2{}_{}{}^{}\Pi _{\mathrm{g}}^{}{}_{}{}^{}$ ground state. A doublet structure, due to spin-orbit coupling, is observed. The fine structure of ${\mathrm{O}}_2^{-}$ is measured to be 0.020 ± 0.002 eV, and the energy of the center of the $v^{\prime }=4\mathrm{}$ resonance doublet is measured to be 0.091 ± 0.005 eV.