J. Combourieu

Kinetic study of the reactions of Cl atoms with HNO3, H2O2, and HO2

The kinetics of the reactions of Cl atoms with HNO3, H2O2, and HO2 have been studied by the discharge flow–mass spectrometric technique. The following rate constants were obtained (in cm3 molecule−1⋅s−1): Cl+HNO3→HCl+NO3, k=1.5 ×10−11 exp(−8700/RT) in the range 298–633 K; Cl+H2O2 →HCl+HO2, k= (4.0±0.4) ×10−13 at 298 K; Cl+HO2→HCl +O2, k= (6.8±2.5) ×10−11 at 298 K. The stratospheric implication of these data is discussed, and it is estimated that the Cl+HO2 reaction could have a comparable effect to the Cl+CH4 reaction as a sink of chlorine atoms in the stratosphere.

EPR kinetic study of the reactions of F and Br atoms with H2CO

Abstract The absolute rate constants of the reactions F + H 2 CO → HF + HCO (1) and Br + H 2 CO → HBr + HCO (2) have been measured using the discharge flow reactor-EPR method. Under pseudo-first-order conditions (¦H 2 CO¦⪢¦F¦or¦Br¦), the following values were obtained at 298 K: k 1 = (6.6 ± 1.1) × 10 −11 and k 2 = (1.6± 0.3) × 10 −12 , Units are cm 3 molecule −1 s −1 . The stratospheric implication of these data is discussed and the value obtained for k makes reaction (2) a possible sink for Br atoms in the stratosphere.

Determination of the rate constants of the reactions of N3 and NCl free radicals using a simulation technique

Abstract A numerical integration method was used to solve the mathematical system corresponding to the mechanism of the reaction of Cl atoms with chlorine azide, N 3 Cl. The identification of calculated kinetic curves of the species involved in the mechanism with the experimental curves led to the determination of rate constants of the following secondary reactions: (2) Cl + N 3 → NCl + N 2 (3) N 3 + N 3 → 3N 2 (4) NCl + NCl → N 2 + Cl 2 At 298K, the rate constants were found to be k 2 : 0.75 – 1.5 × 10 −11 , k 3 : 5 – 8 × 10 −11 , and k 4 : 0.5 – 1 × 10 −11 (units are cm 3 molecule −1 sec −1 ).

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.

Reaction Cl+N3Cl and reactivity of N3, NCl and NCl2 radicals in relation to the explosive decomposition of N3Cl

The reaction kinetics of chlorine atoms with chlorine azide, N3Cl, was studied at pressures near 1 torr in a discharge flow reactor coupled to a quadrupole mass spectrometer adapted to the analysis of free radicals. The rate constant of the initial step: Cl+N3ClN3+Cl2 (1) was found to be k1=2.3×10−11 exp (−1100/RT) cm3 molecule−1 sec−1 between 300 and 657 K. N3, NCl and NCl2 free radicals, produced from the Cl+N3Cl reaction, were detected by mass spectrometry. The mass spectrometric study of these radicals and the determination of stoichiometry showed evidence for the secondary reactions of N3, NCl and N3Cl. The rate constant of the reaction: NCl+Cl2NCl2+Cl (5) was determined as k5=(1.0±0.2)×10−12 cm3 molecule−1 sec−1 at room temperature. The thermal decomposition of N3Cl was studied between 600 and 850 K in the same flow reactor heated isothermically. The NCl radical was mass spectrometrically detected as an intermediate of the decomposition. Kinetic data were obtained showing at least partly heterogeneous character of the decomposition. All these results made it possible to discuss some aspects of the mechanism of the explosive decomposition of N3Cl and more especially of the initial stage of this decomposition.

Reaction of H atoms with CH2Cl2application to the inhibition of flames

The reaction kinetics of atomic hydrogen with dichloromethane have been investigated in adischarge-flow system in the 298°–460°K temperature range, and at total pressures near 1 torr. A quadrupole mass spectrometer was adapted for the simultaneous determination of atomic hydrogen and stable species concentrations. For the H+CH 2 Cl 2 over-all reaction, the stoichiometry[H] 0 −[H]/([CH 2 Cl 2 ] 0 −[CH 2 Cl 2 ]) determined for various initial [H] 0 /[CH 2 Cl 2 ] 0 ratios always exceeds 4. The products have been identified as HCl, H 2 , CH 4 , C 2 H 2 , and C 2 H 4 . The rate constant of the initial step, H+CH 2 Cl 2 →HCl+CH 2 Cl, was found to be k 1 =1.8×10 −11 exp(−6100/ RT ) cm 3 molecule −1 s −1 from 298° to 460°K. Evidence was found for the occurrence of secondary reactions,H+HCl→Cl+H 2 , Cl+CH 2 Cl 2 →HCl+CHCl 2 . The use of D atoms instead of H atoms gives further information on the reaction mechanism, which is discussed. Reaction (1) may be the inhibiting step in the mechanism of flame inhibition by CH 2 Cl 2 .