Peroxynitrates (ROONO₂) are formed in the degradation ofvolatile organic compounds emitted to the atmosphere and are important because they act as reservoirs of NO₂ and RO radicals.Industrial compounds such as chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs), andhydrofluoroethers (HFEs) lead to the formation of fluorinated peroxynitrates. For example, compounds such as HCFC-225ca (C₂F₅CHCl₂), HFC-227a  (C₃F₇H)and HFC-329p (C₄F₉H) could lead to the formation of C₂F₅OONO₂,C₃F₇OONO₂ and C₄F₉OONO₂,respectively.

In this work we used Density Functional Theory (DFT) to evaluate the ground-state geometric parameters,vibrational frequencies, and the relative populations of the different conformers of each peroxynitrate. These parameters were calculated using the hybrid density functional B3LYP with the 6-311+G* basis set, using the G09 Program package in conjunction with GaussView 5.0. Thermal rate coefficients and their pressure dependence for the unimolecular decomposition of these peroxynitrates were evaluated by standard RRKM theory implemented in the UNIMOL program.

Four different conformers are found in the Potential Energy Surface (PES) for C₃F₇OONO₂ and C₄F₉OONO₂. A qualitative inspection of the PES shows that interconversion between them could involve trajectories needingless than 4 kcal, and that the relative energies are less than 1.8 kcal mol⁻¹ with respect to the more stable conformer. On the other hand, for C₂F₅OONO₂ two different minima are found, with 0.016 Kcal for the interconversión energy between them, so it is expected an appreciable amount of both conformers at room temperature.

The most interesting parameters in peroxynitrates are the X-O−O−N dihedral and the O−N distance. Previous studies show that the dihedral is around 105° for this kind of peroxynitrates.The calculated value of this parameter is 104.5° for C₂F₅OONO₂ and 104.7º for C₃F₇OONO₂ and C₄F₉OONO₂. The N−O distance, extremely long in peroxynitrates, takes values of 1.56 Å for this family.

RRKM calculation for the thermal decomposition rate constant show a good agreement with the reported experimental values. The dependence of the rate constant withthe pressure decreases with the length of the carbon chain for pressures higher than 1 mbar. For pressures lower than 1 mbar the dependence with the length ofthe carbon chain is reversed.