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Temperature dependence of the reactions of HO 2 with NO and NO 2
Author(s) -
Simonaitis R.,
Heicklen Julian
Publication year - 1978
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/kin.550100106
Subject(s) - chemistry , arrhenius equation , photodissociation , radical , reaction rate constant , analytical chemistry (journal) , chemical kinetics , negative temperature , reaction rate , reaction mechanism , kinetics , activation energy , thermodynamics , photochemistry , organic chemistry , physics , quantum mechanics , catalysis
Abstract Mixtures of N 2 O, H 2 , O 2 , and trace amounts of NO and NO 2 were photolyzed at 213.9 nm, at 245°–328°K, and at about 1 atm total pressure (mostly H 2 ). HO 2 radicals are produced from the photolysis and they react as follows:Reaction (1b) is unimportant under all of our reaction conditions. Reaction (1a) was studied in competition with reaction (3) from which it was found that k 1a / k 3 1/2 = 6.4 × 10 −6 exp { z−(1400 ± 500)/ RT } cm 3/2 /sec 1/2 . If k 3 is taken to be 3.3 × 10 −12 cm 3 /sec independent of temperature, k 1a = 1.2 × 10 −11 exp {−(1400 ± 500)/ RT } cm 3 /sec. Reaction (2a) is negligible compared to reaction (2b) under all of our reaction conditions. The ratio k 2b / k 1 = 0.61 ± 0.15 at 245°K. Using the Arrhenius expression for k 1a given above leads to k 2b = 4.2 × 10 −13 cm 3 /sec, which is assumed to be independent of temperature. The intermediate HO 2 NO 2 is unstable and induces the dark oxidation of NO through reaction (−2b), which was found to have a rate coefficient k −2b = 6 × 10 17 exp {−26,000/ RT } sec −1 based on the value of k 1a given above. The intermediate can also decompose viaReaction (10b) is at least partially heterogeneous.