Gas-phase reactions between RO2 and NO, HO2 or CH3O2: correlations betweenrate constants and the SOMO energy of the peroxy (RO2) radical

This paper presents correlations between the logarithm of the rate constant s of the reaction between RO2 + NO and RO2 + HO2 (and possibly RO2 + CH3O2) and the singly occupied molecular orbital (SOMO) energy of the organic per oxy radical, RO2. These reactions are of the utmost importance in the tropo spheric oxidation cycle of organic compounds. A correlation such as this ma y allow the prediction of rate constants for the reactions of organic perox y radicals, RO2. with species such as NO, HO2 and CH3O2 where no previous e xperimental determination has been undertaken. The mathematical form of the correlation for the reactions of RO2 with NO and HO2 is - ln k (cm(3) mole cule (- 1) s (- 1)) = mE(SOMO)(RO2) + c, where m = 1.14 and - 1.45 eV (- 1) , c = 28.80 and 21.16 for NO and HO2, respectively; E-SOMO(RO2) is the SOMO energy of the organic RO2 radical in eV. The origin of the correlation is explained in terms of frontier orbital theory. Six previously unmeasured ra te constants are predicted for reactions between RO2 and NO, and 20 rate co nstants are predicted for the reactions between RO2 and HO2. This appears t o be the first time that such a correlation has been applied to a series of radical-radical reactions, and the method holds promise for further chemic al systems. (C) 2001 Elsevier Science Ltd. All rights reserved.