Dissociation Pathways of Peroxyacetyl Nitrate (PAN)

The principal unimolecular dissociation pathways for PAN (peroxyacetyl nitrate, CH 3 C(O)OONO 2 ) have been studied using a variety of theoretical methods. Reaction enthalpies calculated with the complete basis set (CBS) method were evaluated against a set of atmospheric free radical reactions for which the experimental thermochemistry is well defined. The validation procedure, which included two decomposition channels for HOONO 2, demonstrated that the CBS-Q method reproduced the experimental Δ values with a rms error of 5.7 kJ mol -1 . We report new Δ values for PAN, CH 3 C(O)O 2, and CH 3 C(O)O of −240.1, −154.4 and −192.5 kJ mol -1, respectively. Accurate structural calculations for PAN, HOONO 2, CH 3 C(O)O 2, and CH 3 C(O)O augment the thermochemical calculations and show that the B3LYP density functional method describes the chemical bonding in the −OONO 2 linkage quite well. The implications of this study for the atmospheric decomposition of PAN are discussed.