A theoretical study of the thermal stability of the FS(O2)OSO2 radical and the recombination kinetics with the FSO3 radical

Abstract

The kinetics of the thermal reaction of FS(O2)OO(O2)SF with SO2 have been theoretically studied. Experimental investigations performed at 293–323 K indicate that the FSO3 radical, in equilibrium with the peroxide FS(O2)OO(O2)SF ⇄ 2 FSO3 (1, -1), initially attacks the SO2 forming the FS(O2)OSO2 radical which afterwards may dissociate back, FSO3 + SO2 ⇄ FS(O2)OSO2 (2, -2), or recombine with FSO3 generating the final product, FSO3 + FS(O2)OSO2 → (FS(O2)O)2SO2 (3). Several DFT formulations and composite ab initio models were employed to characterize FS(O2)OSO2 molecular properties and to determine relevant potential energy surfaces features of reactions (2), (-2) and (3). Transition state theory calculations lead to the high pressure rate coefficients k∞,2=9.1×10-14exp(-5.2kcal mol-1/RT)cm3molecule-1s-1 and k∞,-2=4.9×1015exp(-13.9kcal mol-1/RT)s-1 while statistical adiabatic channel model (SACM/CT) calculations predict for the barrierless reaction (3) the expression k∞,3=2.9×10-11(T/300)0.4cm3molecule-1s-1. The experimental phenomenological rate coefficients are very well reproduced by these rate coefficients.