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

The kinetics and the mechanism of the 248 nm laser flash photolysis of oxalyl fluoride, (FCO)(2), in the presence of O-2, F-2 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 coefficient values of (3.4 +/- 0.7) x 10(-15) and (4.5 +/- 0.7) x 10(-12) cm(3) molecule(-1) s(-1) were determined for the reactions FC(O)O-2 + F-2 --> FC(O)OOF + F and FC(O)O-2 + F --> FC(O)O-2 + F-->FC(O)+OF whereas the upper limits of 1x10(-17) and 9 x 10(-14) cm(3)molecule(-1)s(-1) were estimated for FC(O)O+F-2 --> FC(O)OF + F and FC(O)O + FO2 --> FC(O)OF + O-2. From isodesmic reaction schemes at the B3LYP/6311++G(d,p) level of theory, the enthalpies of formation of FCO, FC(O)OF, FC(O)OOF and FC(O)OOO(O)CF were 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 us to establish that the reaction between F atoms and FC(O)O-2 proceeds through the formation of an energized complex FC(O)OOF towards FC(O)O and OF in agreement with the experiments. (C) 2000 Elsevier Science B.V. All rights reserved.