Light emission from reaction of atomic oxygen with nitric oxide at low pressures

Abstract

The intensity I_o of chemiluminescent emission by NO₂ produced from the reaction of atomic oxygen with nitric oxides has been reinvestigated in the pressure range 10–250 µ Hg using a fast flow system. The equation I=I_o[O][NO] was obeyed down to pressures of 60 µ Hg. At lower values the light emission became pressure-dependent. The results are explained in terms of a three-body mechanism : O + NO + M → NO^†g ₂+ M (1a), O + NO + M → NO^* ₂+ M (1b), NO^* ₂+ M → NO^† ₂+ M (2), NO^* ₂→ NO₂+hv(3), where † and ^* represent vibrationally and electronically excited species respectively. The quenching constant k₂/k₃ is calculated as 67 torr^–1 and k₂ is estimated as 5 × 10^–11 cm³molecule^–1sec^–1. Consideration of these values in conjunction with the known value for the overall rate constant implies that K_1b K_1a. The differences between the present data and that of earlier workers are suggested as arising from the previously neglected losses of atomic oxygen as a result of rapid radial diffusion and wall recombination at low pressures.