Nonequilibrium vibrational populations and dissociation rates of oxygen in electrical discharges

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Nonequilibrium vibrational distributions and dissociation rates of molecular oxygen in both electrical and thermal conditions have been calculated by solving a system of master equations including V-V (vibration-vibration), V-T (vibration-translation) and e-V (electron-vibration) energy exchanges. The dissociation constant under thermal conditions (i.e. without electrons) follows an Arrhenius law with an activation energy of 120 kcal/mole, while the corresponding rates under electrical conditions (5000 ⩽ T e ⩽ 15000 K, 300 ⩽ T g ⩽ 1000 K, 10 11 ⩽ n e ⩽ 10 12 cm −3,5 ⩽ p ⩽ 20 torr) increase with decreasing gas ( T g) and electron ( T e) temperatures and pressure ( p) and with increasing electron density ( n e). These results are explained on the basis of the different interplay of V-V and V-T energy exchanges and are rationalized by means of simplified models proposed in the literature. The accuracy of the present results is discussed paying particular attention to the dependence of V-V and V-T rate coefficients on the vibrational quantum number. A comparison of the calculated dissociation rates with the corresponding ones obtained by the direct electron impact mechanism shows that the present mechanism prevails at low electron and gas temperatures. Finally a comparison is shown between theoretical and experimental dissociation rates under electrical and thermal conditions.