J. L. Jourdain

EPR determination of absolute rate constants for the reactions of h and oh radicals with hydrogen bromide

Abstract The absolute rate constants for the reactions of H atoms and OH radicals with HBr were measured by the discharge flow technique with EPR detection. The rate constants at room temperature are k 1 = (6.3 ± 0.5) × 10 −12 cm 3 molecule −1 s −1 for H + HBr → H 2 + Br and K 2 = (9.2 ± 0.7) × 10 −12 cm 3 molecule −1 s −1 for OH + HBr → H 2 O + Br. There is a discrepancy between measurements carried out by the EPR-discharge flow and flash photolysis-resonance fluorescence techniques.

Discharge flow study of the CH3S + NO2 reaction mechanism using Cl + CH3SH as the CH3S source

Abstract The discharge flow-EPR-mass spectrometric technique has been used to determine the rate constant for the reaction Cl +CH3SH → CH3S + HCl (1). We determined k1 = (1.1 ± 0.4) × 10−10 cm3 molecule−1 s−1 at room temperature and at 0.3 Torr. This reaction was found to be a convenient source of CH3S in discharge flow systems and was used to study the mechanism of the CH3S + NO2 reaction. Rate constants were obtained for the reactions CH3SO + NO2 → CH3SO2 + NO (4) and CH3SO2 + M → CH3 + SO2 + M (5) giving k4 = (3 ± 2) × 10−11 cm3 molecule−1 s−1 and k5 ⩽ 10 s−1 from modelling the experimental profiles of the reactant and products.

KINETIC STUDY OF REACTIONS OF SOME ORGANIC SULFUR COMPOUNDS WITH OH RADICALS

The reactions of OH radicals with the following organic sulfur compounds CH3SCH3, CH3SH, C2H5SH and C4H4S, have been studied by the discharge flow reactor technique associated to EPR and mass spectrometric detection. The products of the reactions of OH with CH3SH and C2H5SH have been studied mass spectrometrically. The results indicate that for both reactions the initial step would be equivalent to an H atom transfer.

Absolute rate constant for the reaction of OH with thiophene between 293 and 473 K

Abstract The rate parameters of the OH + C 4 H 4 S (thiophene) reaction were measured at a pressure of 0.5 Torr in the temperature range 293–473 K by the discharge flow EPR method. The reaction was found to exhibit a negative temperature dependence. The data fit the Arrhenius expression k = (1.3 ± 0.8) × 10 −13 exp[(1750 ± 200)/ T ] cm 3 molecule −1 s −1 . The rate constant of (5 ± 0.4) × 10 −11 at room temperature corresponds to a short lifetime of C 4 H 4 S in the atmosphere.

Determination of the rate parameters and products for the reaction of hydroxyl radicals with nitric acid

The discharge flow‐EPR technique has been used to measure the rate constant and the product distribution for the reaction of OH with HNO3, which is important for stratospheric modeling. The rate constant is found to be (7.3±2)×10−15 exp[876±85)/T] cm3 molecule−1 s−1 in the range 251–403 K. Besides, the in situ titration of NO3 by NO has shown that the reaction of OH with HNO3 only produces NO3 and H2O at room temperature.

Kinetic study of the reaction of OH radicals with nitrosyl chloride as a possible source of ClOH

Abstract The reaction of OH with NOCl has been studied using the discharge flow reaction-EPR technique. The absolute rate constant is k1 = (4.3±0.4)× 10−13 cm3 molecule−1 s−1 at 298 K. A mass spectrometric investigation of the products shows that this reaction occurs via two primary steps, OH + NOCl → NO + ClOH(1a) and OH + NOCl → HONO + Cl (1b) with k1a =k1b.

UV absorption spectrum of ClO(A2Π—X2Π) up to the (1,0) band

Abstract A column density of ClO of 3.7 × 1017 cm−2 has been obtained in a discharge flow reactor. Under these conditions the UV absorption of the (A2Π—X2Π) system of ClO was studied up to the (1,0) band at 312.5 nm. The temperature profiles in the cell were measured and the temperature effect was taken into account in the analysis of the spectra and in the determination of the absorption cross sections.

About the identification of some UV atmospheric absorptions: laboratory study of CIO

Abstract Concentrations of CIO radicals of about 5 × 10 16 radicals cm −12 were produced from the reaction: Cl + CLO 2 → 2ClO in a discharge flow reactor. UV absorption of the A 2 πX 2 π system of CIO was measured in the near UV where there is some possibility of stratospheric CIO being detected. Absorption cross sections were determined.

Kinetic Studies of Oxidation Reactions of Sulfur Compounds: Reaction SO2 + OH in the Presence Of O2, and Reaction IO + DMS

The reactions of atmospheric interest, SO2 + OH in the presence of O2 and IO + DMS, have been studied using the discharge flow method with EPR or mass spectrometric analysis of the species. The following rate constants were measured at room temperature: