Electron Attachment and Detachment. I. Pure O2 at Low Energy

Electron attachment and detachment coefficients are reported for pure oxygen from analyses of the current waveforms observed in drift-tube experiments. The results are consistent with the identification of the negative ion as O2− with an electron affinity of 0.43±0.02 eV. The two-body collisional detachment coefficient for O2− in thermal equilibrium with the gas increases from 9×10−17 cm3/sec at 375°K to 1.4×10−14 cm3/sec at 575°K. The three-body attachment coefficient for thermal electrons increases from 2.0±0.2×10−30 cm6/sec at 300°K to 2.8±0.5×10−30 cm6/sec at 530°K. The O2− ions are found to survive at least 3×108 elastic collisions without de-excitation and so are believed to be in their lowest vibrational state. At low oxygen densities the current of detached electrons is separated from the negative-ion current by applying a high-frequency voltage to the control grid. At high oxygen densities the electrons and negative ions cross the tube in a narrow pulse at a drift velocity determined by the equilibrium concentrations of electrons and ions.