Abstract: The rate constants for the thermal decomposition reaction of peroxyacetyl nitrate (PAN), PAN→CH₃C(O)OO+NO₂(R1) were reestimated by RRKM theory and loosing transition state model based on the optimized structures and energies at the G3MP2B3 level of theory and the results agree with the experiment values. Then using the same models, the rate constants for another thermal decomposition reaction of PAN, PAN→CH₃(O)O+NO₃(R2) were studied. In Troe′s notation, the RRKM curves are presented by the following expressions for the limiting low- and high-pressure rate constants, k₀(1)=8.0×10^-3exp[－11912.8/T] cm³•molecule^-1•s^-1; k<_∞(1)=2.8×10¹⁶16exp[－13531.8/T] s^-1; k₀(2)=6.1×10¹⁶exp[－13011.9/T] cm³•molecule-1•s-1; k_∞(2)=4.0×10¹⁶exp[－15463.1/T] s^{-1. The results of calculation suggested that the reaction R1 is the main dissociation channel, while R2 is the minor one and the difference between the rates of the two reactions is about 102 at the same conditions.}

Key words: Peroxyacetyl nitrate, G3MP2B3, RRKM theory, Rate constant, Loose transition state