Fourier Transform Infrared Spectroscopic Study of the Thermal Stability of Peroxyacetyl Nitrate

Article abstract of DOI:10.1021/j100273a034

The unimolecular decomposition of peroxyacetyl nitrate (PAN) to form methyl nitrate and carbon dioxide has been studied over the temperature range 298-338 K by Fourier transform infrared spectroscopy (FTIR).Pure PAN samples (>98percent; 2-30 torr) were found to decompose thermally, nearly quantitatively, to these products, with the only other observed product being nitromethane (<10percent).Both PAN decomposition and methyl nitrate formation rates yielded the Arrhenius equation, k=(2.1*10¹²)exp(-24.800+/-1800 cal/(K mol/RT)) s^-1.Perdeuterio-PAN was synthesized and observed to decompose to perdeuteriomethyl nitrate and carbon dioxide with no apparent isotope effect.Experiments adding nitric oxide to the PAN are described which confirm the existence of two unimolecular pathways for the decomposition of peroxyacyl nitrates.One pathway is a concerted reaction most likely proceeding via a cyclic intermediate, and the other the previously identified equilibrium between PAN and the peroxyacetyl radical and nitrogen dioxide was determined to be 2.2*10^-4 s^-1 at 298 K.This rate is somewhat slower than previously reported for this pathway.The results are discussed with respect to the atmospheric liftime of PAN and the potential atmospheric production of methyl nitrate.