Quantum chemical study of the atmospheric C2H5C(O)OONO2 (PPN) molecule and of the C2H5C(O)OO and C2H5C(O)O radicals

Ab initio and density functional calculations have been performed on atmospheric peroxypropionyl nitrate, C2H5C(O)OONO2 (PPN) molecule and its radical decomposition products C2H5C(O)OO and C2H5C(O)O. Potential barriers for the internal rotations have been computed at the B3LYP/6-311++G(d,p) level of theory. Geometries, harmonic vibrational frequencies and thermochemical properties of stable rotational conformers and transition states have been calculated at the B3LYP/6-311++G(3df,3pd) and G3MP2B3 levels. For PPN, the results shown a structure in which the atoms nearest to the OO bond are in approximately perpendicular planes, τ(COON) = 85.9°. The standard enthalpies of formation at 298 K have been calculated using isodesmic reactions at the G3MP2//B3LYP/6-311++G(3df,3pd) level of theory. The resulting values for PPN, C2H5C(O)OO, and C2H5C(O)O are −66.5, −43.2, and −46.6 kcal mol−1, respectively. Dissociation enthalpies of 31.5 and 37.5 kcal mol−1 have been predicted for the C2H5C(O)OO-NO2 and C2H5C(O)O-ONO2 bonds from the above enthalpies of formation. For comparative purposes, results derived from similar calculations are also reported for the peroxyacetyl nitrate, CH3C(O)OONO2 (PAN) and for the CH3C(O)OO and CH3C(O)O radicals.