Measurements of the gas phase UV absorption spectrum of C2H5O2· radicals and of the temperature dependence of the rate constant for their self-reaction

Abstract

Abstract A flash photolysis technique has been used to measuer the gas phase UV absorption cross-sections for C 2 H 5 O 2 · radicals over the wavelength range 215 – 300 nm. Kinetic absorption spectroscopy was then employed to study the self-reaction of these radicals. The measured absorption cross-section at 250 nm, (3.89 ± 0.54) × 10 −18 cm 2 molecule −1 , was sued to derive an observed self-reaction rate constant at room temperature, defined as −d[C 2 H 5 O 2 ]·/d t = 2 k obs [C 2 H 5 O 2 ·] 2 , of k obs = (9.87 ± 0.74) × 10 −14 cm 3 molecule −1 s −1 , independent of pressure over the range 25 – 400 Torr. Experiments were performed over the temperature range 228 – 380 K and the kinetic data were fit by the Arrhenius expression ( k obs = (1.41 ± 0.19) × 10 −13 exp{su−(110 ± 40)/ T } cm 3 molecule −1 s −1 ) where the error limits represent 2σ from linear least-squares analysis. A modeling assessment of the effects of secondary reactions involving C 2 H 5 O 2 · radicals indicates that these measured values for k obs could be higher than the true rate constant for the self-reaction by as much as a factor of 1.7 depending on the branching ratio for the various product channels for the reaction C 2 H 5 O 2 · + C 2 H 5 O 2 · → Products. Thus k 1 ≈ (0.6) k obs .