Fine structure of O2+ 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-O₂ scattering corresponding to vibrationally excited levels of the O₂⁻ ${}^2{\Pi }_g$ ground state. A doublet structure, due to spin-orbit coupling, is observed. The fine structure of O₂⁻ is measured to be 0.020 ± 0.002 eV, and the energy of the center of the v′=4 resonance doublet is measured to be 0.091 ± 0.005 eV.