The O( 1S) quantum yield from O 2+ dissociative recombination

Recent laboratory studies show that the O( ¹S) quantum yield, f( ¹S) , from O ₂⁺ dissociative recombination varies considerably with the degree r of vibrational excitation. However, the suggestion that the high values for f( ¹S) deduced from airglow and auroral observations can be explained by invoking vibrational excitation, creates a number of problems. Firstly, the rapid vibrational deactivation of O ₂⁺ ions by collisions with O atoms will keep r too low to account for the magnitude of f( ¹S) ; secondly, r varies considerably from one atmospheric source to another but its relative values (which should be reliable) do not co-vary with those of f( ¹S) ; thirdly, because r increases markedly above the peak of the X5577 Å dissociative recombination layer, the fits which theorists have obtained to the observed volume emission rate profiles would have to be regarded as fortuitious. It is tentatively suggested that f( ¹S) is higher in the airglow and aurora than in the laboratory plasma studied by Zipf (1980) because of the electron temperature dependence of the O( ¹S) specific recombination coefficient for O ₂⁺(v ^' ⩽ 3) ions. The repulsive ¹Σ _u[ ¹D + ¹s] state of O ₂ does not provide a suitable channel for the dissociative recombination. A possible alternative is the bound ³Π _u[ ⁵S + ³s] state with predissociation to the repulsive ³Π _u[ ³P + ¹s] state.