Kinetics of the reaction of FC(O)O2 radicals with F atoms and F2.

BADENES, M. P.; CASTELLANO, E.; COBOS, C. J.; CROCE, A. E.; MARIA EUGENIA TUCCERI

Chemical Physics

Año: 2000 vol. 253 p. 205 - 217

0301-0104

The kinetics and the mechanism of the 248 nm laser flash photolysis of oxalyl fluoride, (FCO)2, in the presence of O2, F2 and the bath gases He and SF6 has been studied at 295 K. The kinetics was followed by monitoring the FC(O)O radical by absorption at 545 nm. Rate coefficients values of (3.4±0.7)x10-15 and (4.5±0.7)x10-12cm3 molecule-1 s-1 were determined for the reactions FC(O)O2+F2-->FC(O)OOF+F and FC(O)O2+F-->FC(O)O+OF while upper limits of 1x10-17 and 9x10-14 cm3 molecule-1 s-1 were estimated for FC(O)O+F2-->FC(O)OF+F and FC(O)O+FO2-->FC(O)OF+O2. From isodesmic reaction schemes at the B3LYP/6-311++G(d,p) level of theory, the enthalpies of formation of FCO, FC(O)OF, FC(O)OOF and FC(O)OOO(O)CF are calculated to be -44.6±2, -102.9±2, -91.2±2 and -186.0±2 kcal mol-1, respectively. Density functional theory and statistical adiabatic channel model calculations allow to establish that the reaction between F atoms and FC(O)O2 proceeds through the formation of an energized complex FC(O)OOF towards FC(O)O and OF in agreement with the experiments.