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

This paper presents correlations between the logarithm of the rate constants of the reaction between RO2+NO and RO2+HO2 (and possibly RO2+CH3O2) and the singly occupied molecular orbital (SOMO) energy of the organic peroxy radical, RO2. These reactions are of the utmost importance in the tropospheric oxidation cycle of organic compounds. A correlation such as this may allow the prediction of rate constants for the reactions of organic peroxy radicals, RO2, with species such as NO, HO2 and CH3O2 where no previous experimental determination has been undertaken. The mathematical form of the correlation for the reactions of RO2 with NO and HO2 is −lnk (cm3molecule−1s−1)=mESOMO(RO2)+c, where m=1.14 and −1.45 eV−1, c=28.80 and 21.16 for NO and HO2, respectively; ESOMO(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 rate constants are predicted for reactions between RO2 and NO, and 20 rate constants are predicted for the reactions between RO2 and HO2. This appears to 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 chemical systems.