The potential energy surfaces for the reaction of pyridinyl radicals with O
-2 have been studied using the B3LYP method. The initial production of the
pyridinylperoxy radical followed by either simple decomposition or rearrang
ement to yield the intermediates (pyridinyloxy, dioxiranylpyridinyl, or dio
xetanylpyridinyl radicals) has been explored. Transition-state structures f
or most of the steps are presented as well as relative free energies over a
range of temperatures from 298 to 2000 K. The energetics of the analogous
intermediates for the reaction of O-2 and other azabenzene radicals derived
from pyridazine, pyrimidine, and pyrazine are also provided. O-2 dissociat
ion from the arylperoxy radical is preferred rather than the loss of O atom
to generate the corresponding aryloxy radical, and this preference is cont
rary to phenylperoxy radical decomposition. However, the formation of a dio
xiranyl radical intermediate is the most accessible intermediate from the p
eroxy precursor at temperatures less than or equal to 500 K. Dioxetanyl int
ermediates are less favored but may provide a route to NOx generation from
nitrogen substitution in aromatic fuels.