Kinetic study of the F2 + C2H4 reaction: Disagreement between theory and experiment resolved?

International audienc

Kinetics and Mechanism of the Reaction of Cl Atoms with HO 2 Radicals

ABSTRACT: The kinetics and mechanism of the reaction Cl ϩ HO 2 : products (1) have been studied in the temperature range 230-360 K and at total pressure of 1 Torr of helium using the discharge-flow mass spectrometric method. The following Arrhenius expression for the total rate constant was obtained either from the kinetics of HO 2 consumption in excess of Cl atoms or from the kinetics of Cl in excess of HO 2 : , where uncertainties are 95% confidence limits. The temperature-independent value of k 1 ϭ (4.4 Ϯ 0.6) ϫ 10 Ϫ11 cm 3 molecule Ϫ1 s Ϫ1 at T ϭ 230-360 K, which can be recommended from this study, agrees well with most recent studies and current recommendations. Both OH and ClO were detected as the products of reaction (1) and the rate constant for the channel forming these species, Cl ϩ HO 2 : OH ϩ ClO (1b), has been determined: k 1b ϭ (8.6 Ϯ 3.2) ϫ 10 Ϫ11 exp[Ϫ(660 Ϯ 100)/T] cm 3 molecule Ϫ1 s Ϫ1 (with k 1b ϭ (9.4 Ϯ 1.9) ϫ 10 Ϫ12 cm 3 molecule Ϫ1 s Ϫ1 at T ϭ 298 K), where uncertainties represent 95% confidence limits

Temperature-Dependent Kinetic Study of the Reactions of Hydrogen Atoms with H₂S and C₂H₄S

A discharge-flow reactor combined with modulated molecular beam mass spectrometry technique was employed to determine the rate constants of H-atom reactions with hydrogen sulfide and thiirane. The rate constants for both reactions were determined at a total pressure of 2 Torr from 220 to 950 K under pseudo-first-order conditions by monitoring either consumption of H atoms in excess of H2S (C4H4S) or the molecular species in excess of atomic hydrogen. For H + H2S reaction, a suggested previously strong curvature of the Arrhenius plot was confirmed: kl = 8.7 × 10−13 × (T/298)2.87 × exp(−125/T) cm3 molecule−1 s−1 with a conservative uncertainty of 15% at all temperatures. Non-Arrhenius behavior was also observed for the reaction of H-atom with C2H4S, with the experimental rate constant data being best fitted to a sum of two exponential functions: k2 = 1.85 × 10−10 exp(−1410/T) + 4.17 × 10−12 exp(−242/T) cm3 molecule−1 s−1 with an independent of temperature uncertainty of 15%

Rate Constant of the Reaction of OH Radicals with HBr over the Temperature Range 235–960 K

International audienceThe kinetics of the reaction of hydroxyl radicals with HBr, important in atmospheric and combustion chemistry, has been studied in a discharge flow reactor combined with an electron impact ionization quadrupole mass spectrometer in the temperature range 235–960 K. The rate constant of the reaction OH + HBr → H2O + Br (1) was determined using both a relative rate method (using the reaction of OH with Br2 as a reference) and absolute measurements, monitoring the kinetics of OH consumption under pseudo-first-order conditions in excess of HBr. The observed U-shaped temperature dependence of k1 is well represented by the sum of two exponential functions: k1 = 2.53 × 10–11 exp(−364/T) + 2.79 × 10–13 exp(784/T) cm3 molecule–1 s–1 (with an estimated conservative uncertainty of 15% at all temperatures). This expression for k1, recommended for T = 240–960 K, combined with that from previous low temperature studies, k1 = 1.06 × 10–11 (T/298)−0.9 cm3 molecule–1 s–1 at T = 23–240 K, allows to describe the temperature behavior of the rate constant over an extended temperature range 23–960 K. The current direct measurements of k1 at temperatures above 460 K, the only ones to date, provide an experimental dataset for use in combustion and volcanic plume modeling and an experimental basis to test theoretical calculations

Rate constants for the reaction of SO with NO 2 over the temperature range 220–960 K

International audienceThe kinetics of the reaction of SO radicals with NO2 have been studied in a discharge flow reactor combined with an electron impact ionization quadrupole mass spectrometer at nearly 2 Torr total pressure of helium and in the temperature range 220–960 K. The reaction rate constant was determined under pseudo-first order conditions in excess of NO2 over SO using two different methods for generation of the SO radicals: k1 = (6.7 ± 0.2) × 10−12 exp(295 ± 10)/T) cm3 molecule−1 s−1 (the uncertainties represent precision at the 2σ level, the estimated total uncertainty on the rate constant being 15% at all temperatures). The present measurements indicate that the current recommendations for k1 underestimate the rate constant at low stratospheric temperatures and overestimate it at the high temperatures characteristic of combustion

Temperature dependent rate constant for the reaction of H‐atoms with carbonyl sulfide

International audienceAbstract The kinetics of the reaction of H‐atom with carbonyl sulfide (OCS) has been investigated at nearly 2 Torr total pressure of helium over a wide temperature range, T = 255–960 K, using a low‐pressure discharge flow reactor combined with an electron impact ionization quadrupole mass spectrometer. The rate constant of the reaction H + OCS → SH + CO (1) was determined under pseudo‐first order conditions, monitoring the kinetics of H‐atom consumption in excess of OCS, k 1 = 6.6 × 10 −13 × ( T /298) 3 × exp(−1150/ T ) cm 3 molecule −1 s −1 (with estimated total uncertainty on k 1 of 15% at all temperatures). Current measurements of k 1 at intermediate temperatures (520–960 K) appear to reconcile previous high and low temperature data and allow the above expression for k 1 to be recommended for use in the extended temperature range between 255 and 1830 K with a conservative uncertainty of 20%

Kinetics and Products of the Reactions of Fluorine Atoms with ClNO and Br 2 from 295 to 950 K

International audienc

Reaction F + C 2 H 4 : Rate Constant and Yields of the Reaction Products as a Function of Temperature over 298–950 K

International audienc

Reaction of O( 3 P) with Carbon Disulfide: Kinetics and Products

International audienceThe kinetics and products of the reaction of ground-state O atoms with carbon disulfide, of interest for atmospheric and combustion chemistry, were studied using a discharge-flow system combined with modulated molecular beam mass spectrometry. The total reaction rate constant was determined in an absolute way from kinetics of CS2 consumption and reaction product, SO radical formation, and employing a relative rate method with two reference reactions: k1 = (3.35 ± 0.10) × 10–11 exp(−(665 ± 15)/T) cm3 molecule–1 s–1 at T = 220–960 K, with an estimated independent of temperature uncertainty of 15%. The yields of two reaction products, SO and OCS, were determined at T = 220–960 K, resulting in the following expressions for the branching ratio of the corresponding (SO + CS and OCS + S forming) reaction pathways: k1a/k1 = (0.935 ± 0.005) × exp(−(7.4 ± 0.2)/T) and k1b/k1 = (0.067 ± 0.002) × exp(80 ± 8/T), where the uncertainties reflect the statistical 2σ precision. The reaction rate constant and product data from the present work are discussed in comparison with previous experimental and theoretical studies

Rate constant of H atom reaction with Br2 determined between 220 and 950 K

Rate constant of the reaction H + Br2 → HBr + Br (1) has been measured in a discharge flow reactor with mass spectrometric monitoring of the species involved: k1 = 7.06 × 10−11 (T/298)0.88 exp(182/T) cm3 molecule−1 s−1 at T = 220 – 950 K (with estimated total uncertainty on the rate constant of 15% at all temperatures). The kinetic data in the present work challenge previous experimental measurements and support the most recent theoretical calculation