Ts. Dibble et Js. Francisco, THE LAST CHAPTER ON CHLOROFLUOROCARBON PHOTOOXIDATION PROCESSES - FORMATION AND DISSOCIATION OF FC(O)ONO, Journal of physical chemistry, 98(19), 1994, pp. 5010-5018
The key features of the potential energy surface of FC(O)ONO and its F
C(O)NO2 isomer have been determined using ab initio molecular orbital
theory. This species, which may be regarded as the NO adduct of the FC
(O)O radical, is postulated to be an intermediate in the atmospheric d
egradation of chlorofluorocarbons. Hartree-Fock (HF) and second-order
Moller-Plesset perturbation theory (MP2) are used to characterize the
structure and vibrational frequencies of two FC(O)ONO chain conformers
and two higher energy isomers, including a stable cyclic species whos
e structure can be represented as FN[(O)(O)]C=O. Relative energies are
determined using MP4 and QCISD(T) (quadratic configuration interactio
n with single, double, and triple excitations) methods. Transition sta
tes are found connecting the two FC(O)ONO chain conformers to each oth
er, to FC(O)NO2, and to stable degradation products. The exothermicity
of formation of FC(O)ONO by any pathway is more than sufficient to ov
ercome the barrier to formation of FNO + CO2, the most exothermic spec
ies on the entire potential energy surface. Thus, the reaction of FC(O
)O-x radicals with NOx radicals terminates chlorofluorocarbon photooxi
dation by converting FC(O)O, radicals to CO2 and FNO, which is suggest
ed as a hitherto undetected fluorine reservoir species.