Infrared Absorption by Peroxy-Nitrogen Trioxide Free Radical in the Gas Phase

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Abstract
In the course of studying the low‐pressure thermal oxidation of nitric oxide by oxygen, a new absorption band occurring on the shoulder of the P branch of nitric oxide at 1840 cm−1 was observed. The new absorption band was shown to be first order with respect to both nitric oxide and oxygen. The variation of this absorption band with time indicated that it was probably due to the free‐radical intermediate present in this system, and was assigned to peroxy‐nitrogen trioxide. The structural assignment OONO, rather than the symmetrical nitrate radical is based on the absorption frequency and by a comparison with frequencies expected for OONO and symmetrical NO3. By assuming a value for the absorption coefficient of OONO, which is presumably formed by the rapid reversible reaction O2+NO⇌OONO, thermodynamic data concerning OONO and the equilibrium constant were estimated.