Study of ClCH2CH2O2 using modulated photolysis: Ultra-violet spectrum and self-reaction kinetics

Abstract

By use of the modulated photolysis technique, the ultraviolet absorption spectrum and the kinetics of the self-reaction have been studied for chloroethylperoxy radical. Results are obtained in the temperature range 253–345 K and pressure range 50–200 Torr. At room temperature, the value of the observed rate constant k_obs (cm³ molecule⁻¹ s⁻¹) is found to be: k_obs = (4.5 ± 0.4) × 10⁻¹², and the Arrhenius expression for this parameter is: k_obs(T) = (4.0 ± 1.3) × 10⁻¹⁴exp(1376 ± 60/T). This effective constant, defined as −d[ClCH₂CH₂O₂]/dt = 2k_obs[ClCH₂CH₂O₂]² corresponds to the global consumption of ClCH₂CH₂O₂ radical via the reactions: ClCH₂CH₂O₂ + ClCH₂CH₂O₂ → ClCH₂CH₂O + ClCH₂CH₂O + O₂                →ClCH₂CH₂OH + ClCH₂CHO + O₂    ClCH₂CH₂O₂ + HO₂ → ClCH₂CH₂O₂H + O₂

Using the branching ratio for the mutual reactions (Ia) and (Ib) of chloroethylperoxy radical—known at 298 K—the values of this parameter at 253 K and 345 K are deduced and the kinetic parameters of reactions (Ia), (Ib) and (VI) are evaluated at these three temperatures. Approximate Arrhenius expressions are proposed for these rate constants. On the basis of the reaction mechanism, the simulation of all our experimental observations is carried out with good precision and the spectrum of ClCH₂CH₂OOH is determined. Our values confirm those of previous studies with good agreement. From these results we observe the effect of the peroxy radical structure on its reactivity.