Proton affinity of peroxyacetyl nitrate (PBN)

Ab initio calculations for the proton affinity of peroxyacetyl nitrate (PAN ) reveal the complicated protonation chemistry; associated with the unusual multifunctional structure of this molecule. Optimized molecular structures , relative energies, decomposition energies, and proton affinities have bee n determined for four chemically distinguishable PANH(+) protomers. Calcula tions performed at the CBS-Q level of theory predict that the most stable s tructure is the peracetic acid-nitronium ion complex, [(CHC)-C-3(O)OOH . . . NO2+] and yield PA(CBS-Q)(0K)(PAN) = -773.4 +/- 10 kJ mol(-1). This resul t disagrees with the experimental determination of PA(298 K)(PAN) = -798 +/ - 12 kJ mol(-1) that was attributed to protonation of the carbonyl oxygen b ut agrees with the experimental and theoretical results for the proton affi nities of the nitrates HONO2, CH3ONO2, C2H5ONO2, and HOONO2, where the most stable protomers an also of the form [ROH . . . NO2+].