KINETIC AND THERMODYNAMIC PROPERTIES OF THE F+O-2 REACTION SYSTEM UNDER HIGH-PRESSURE AND LOW-TEMPERATURE CONDITIONS

The reaction F+O2+M→FOO+M(1) in the bath gases M=He, Ar, and N2 was studied by time-resolved uv absorption spectroscopy of the FOO radical at 220 nm. The experiments were performed at total pressures between 1 and 1000 bar and temperatures between 100 and 420 K. The absorption cross section of FOO was determined as σ (300 K) = 1.6.10-17 cm21 at 220 nm. The F O2 bond energy was derived by third law analysis of the equilibrium constant K1 = 9.15.10 -24.T-0.45.exp(5990 K/T) cm3 (between 315 and 420 K) for reaction (1), being (49.8±1) kJ mol-1 (at 0 K). Limiting low pressure rate constants for the recombination reaction (1) of k1;0/[He]=3.7.10-33.(T/300 K)-1.1 cm 6 s-1, k1,0/[Ar]=4.4.10-33.(T/300 K)-1.4 cm6 s-1, and k1,0/[N 2]=5.8.10-33.(T/300 K)-1.7 cm6 s_1 were obtained between 100 and 373 K. The transition to a high pressure plateau of the rate constants was observed in all cases although the transition to diffusion-controlled reaction may have been superimposed at very high pressures. Correcting for this effect, a limiting high pressure rate constant of k1,∞=1.2.10-10 cm3 s _1 was derived between 100 and 373 K. In addition, a rate constant for the reaction F+FOO→F2+O2(2) of k2 = 1.4.10-9 exp(-2790 Y/T) cm3 s_1 (340-420 K) with an uncertainty of Δk2/k2 = ±10% was derived. Furthermore, an equilibrium constant for the reaction F+FOO↔F 2O2(3) of K3 = (1.9±0.7).10 -15 cm3 was obtained at 340 K. © 1995 American Institute of Physics.