Showing papers by "Robert Lesclaux published in 1996"
TL;DR: In this article, the rate constant k1 was determined between 273 and 460 K from the formation rate of CCl2O in the Cl atom initiated oxidation chain of chloroform, where reaction 1 was the rate-limiting step; k1 = (3.3 ± 0.6) × 10-13 exp[(745 ± 58)K/T] cm3 molecule-1 s-1.
Abstract: The kinetics and mechanism of the reactions CCl3O2 + CCl3O2 → 2CCl3O + O2 (1), CHCl2O2 + CHCl2O2 → 2CHCl2O + O2 (2a), CHCl2O2 + CHCl2O2 → CHCl2OH + CCl2O + O2 (2b), CCl3O2 + HO2 → products (3), and CHCl2O2 + HO2 → products (4) have been investigated as a function of temperature at total pressures of 700−760 Torr. Two complementary techniques were used: flash photolysis/UV absorption for kinetic measurements and continuous photolysis/FTIR spectroscopy for end-product analyses. The UV absorption spectra of CHCl2O2 and CCl3O2 were determined between 220 and 280 nm; they have shapes similar to those of other alkyl peroxy radicals, but with broader and less intense bands. The rate constant k1 was determined between 273 and 460 K from the formation rate of CCl2O in the Cl atom initiated oxidation chain of chloroform, where reaction 1 was the rate-limiting step; k1 = (3.3 ± 0.6) × 10-13 exp[(745 ± 58)K/T] cm3 molecule-1 s-1, where quoted (1σ) errors represent only statistical uncertainties. Reaction 2 proceeds ...
78 citations
TL;DR: A flash photolysis technique was used to measure the UV absorption spectrum of the peroxy radical (CH3)2C(OH)CH2O2 formed in the CH3)3COH/Cl/O2 reaction system and to study the kinetics of its self reaction and reaction with the HO2 radical at room temperature and above as mentioned in this paper.
Abstract: A flash photolysis technique was used to measure the UV absorption spectrum of the peroxy radical (CH3)2C(OH)CH2O2 formed in the (CH3)3COH/Cl/O2 reaction system and to study the kinetics of its self reaction and reaction with the HO2 radical at room temperature and above: 2(CH3)2C(OH)CH2O2 → 2(CH3)2C(OH)CH2O + O2 (5a); 2(CH3)2C(OH)CH2O2 → (CH3)2C(OH)CH2OH + (CH3)2C(OH)CHO + O2 (5b); (CH3)2C(OH)CH2O2 + HO2 → (CH3)2C(OH)CH2OOH + O2 (8). The spectrum of the radical resembles that of other β-hydroxyl substituted peroxy radicals in form and magnitude. Use of this and other known absorption cross sections in an appropriate chemical model of the system allowed k5, the branching ratio α (=k5a/k5), and k8 to be derived as a function of temperature (T = 306−398 K) by an iterative procedure involving the simulation of experimental decay traces recorded at several wavelengths: k5 = (1.4 ± 0.6) × 10-14 exp[(1740 ± 150)K/T) cm3 molecule-1 s-1; α = 0.59 ± 0.15 (no discernible temperature dependence over this range); k...
25 citations
TL;DR: In this article, a laser flash photolysis technique has been used to study the kinetics of the following reactions of the allylperoxy radical at atmospheric pressure and as a function of temperature.
Abstract: The laser flash photolysis technique has been used to study the kinetics of the following reactions of the allylperoxy radical at atmospheric pressure and as a function of temperature: CH2CHCH2O2+ CH2CHCH2O2→ products (1), CH2CHCH2O2+ HO2→ CH2CHCH2O2H + O2(2) The radicals were generated by the photolysis of suitable hexa-1,5-diene–O2–N2 and 3-chloropropene–HCHO–O2–N2 mixtures at λ= 193 nm, the resulting total absorbance being measured as a function of time by UV absorption spectrometry. Knowledge of the secondary chemistry and of radical and product absorption spectra, combined with reasonable assumptions of their variations with temperature, allowed the rate coefficients of interest to be estimated by an iterative procedure involving numerical integration of decay profiles recorded at appropriate analysis wavelengths. The resulting Arrhenius expression for reaction (1) is k1=(5.4 ± 1.1)× 10–14 exp[(760 ± 70)/T] cm3 molecule–1 s–1(T= 286–394 K), yielding k1(296 K)=(7.0 ± 0.2)× 10–13 cm3 molecule–1 s–1 and in very good agreement with the only other room-temperature measurement of this rate coefficient (M. E. Jenkin et al., J. Chem. Soc., Faraday Trans., 1993, 89, 433). The determination of k2 was limited by experimental conditions to T= 393–426 K, within which no variation with temperature could be distinguished, and giving k2=(5.6 ± 0.4)× 10–12 cm3 molecule–1 s–1. Extrapolation to 298 K then suggests k2≈ 1 × 10–11 cm3 molecule–1 s–1. The implications of these results for our understanding of isoprene degradation under conditions of low NOx concentrations and for general trends in peroxyl radical reactivity are discussed.
19 citations