Kinetics of the reactions of FC(O)O-2 radicals with F atoms and F-2

The kinetics and the mechanism of the 248 nm laser flash photolysis of oxal yl fluoride, (FCO)(2), in the presence of O-2, F-2 and the bath gases He an d SF6 has been studied at 295 K. The kinetics was followed by monitoring th e 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, -1 02.9 +/- 2, -91.2 +/- 2 and -186.0 +/- 2 kcal.mol(-1), respectively. Densit y functional theory and statistical adiabatic channel model calculations al low 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 ri ghts reserved.