AbstractSpectroscopic studies of the airglow indicate that electronically excited molecular oxygen in the1Δgand1Σg+states is produced in the atmosphere. The way in which the excited states are formed in the atmosphere has been the subject of much speculation, and the present paper attempts to evaluate some of the mechanisms proposed in the light of laboratory experiments.The most probable excitation mechanism for O2(1Δg) appears to be the primary step in the photolysis of atmospheric ozone:O3+ hν (λ<3,100 Å) → O2(1Δg) + (1D).O2(1Δg+) may then be formed in the energy‐pooling process:O2(1Δg) + O2(1Δg) → O2(1