Quantum chemical study of the atmospheric C 2H 5C(O)OONO 2 (PPN) molecule and of the C 2H 5C(O)OO and C 2H 5C(O)O radicals

Abstract

Ab initio and density functional calculations have been performed on atmospheric peroxypropionyl nitrate, C 2H 5C(O)OONO 2 (PPN) molecule and its radical decomposition products C 2H 5C(O)OO and C 2H 5C(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 O O 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, C 2H 5C(O)OO, and C 2H 5C(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 C 2H 5C(O)OO–NO 2 and C 2H 5C(O)O–ONO 2 bonds from the above enthalpies of formation. For comparative purposes, results derived from similar calculations are also reported for the peroxyacetyl nitrate, CH 3C(O)OONO 2 (PAN) and for the CH 3C(O)OO and CH 3C(O)O radicals.