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The dissociative attachment cross section for production of O- by electron impact on the metastable O2 (a1 Δ g) state is studied. The cross section is found to be 4.6 ± 1.3 × 10-18 cm2 at its maximum. From the measured energy dependence, we infer that the dissociative attachment process takes place through the O2̅ (2 Пu) state as in the case of O- production from the O2 ground state. The information thus obtained is used to estimate the portion of the cross section for excitation of the a1 Δg state by electron impact which proceeds via the O2-(2 Пu) state. This mechanism is shown to account for the location and approximate magnitude of the maximum in the excitation cross section. Finally, information is obtained concerning the cross section for positive ionization of the O2 (a- Δg) state near threshold.