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Self‐Reaction of HO 2 and DO 2 : Negative temperature dependence and pressure effects
Author(s) -
Mozurkewich Michael,
Benson Sidney W.
Publication year - 1985
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.550170802
Subject(s) - chemistry , kinetic isotope effect , ammonia , decomposition , adduct , thermodynamics , negative temperature , transition state theory , hydrogen , activation energy , reaction rate constant , atomic physics , deuterium , kinetics , organic chemistry , physics , quantum mechanics
The negative temperature dependence, pressure dependence, and isotope effects of the self‐reaction of HO 2 are modeled, using RRKM theory, by assuming that the reaction proceeds via a cyclic, hydrogen‐bonded intermediate. The negative temperature dependence is due to a tight transition state, with a negative threshold energy relative to reactants, for decomposition of the intermediate to products. A symmetric structure for this transition state reproduces the observed isotope effect. The weak pressure dependence for DO 2 self‐reaction is due to the approach to the high‐pressure limit. Addition of a polar collision partner, such as ammonia or water vapor, enhances the rate by forming an adduct that reacts to produce deexcited intermediate. A detailed model is presented to fit the data for these effects. Large ammonia concentrations should make it possible to reach the high‐pressure limit of the self‐reaction of HO 2 .