Rate constant of the BrO + BrO reaction over the temperature range 220‐950 K

et al. 2021

ACS Earth Space Chem.

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Epoxides have many primary and secondary atmospheric sources. As with other oxygenates, they exhibit a complex temperature-dependent reaction with OH, whose full description is necessary in order to understand their interactions in atmospheric and combustion environments. We measured the kinetics of the title reaction using two complementary absolute methods: pulsed-laser photolysis–laser-induced fluorescence (PLP–LIF) and a discharge-flow mass spectrometric system (DF-MS), both monitoring temporal decays in OH. In addition, two relative methods employing the DF-MS as a function of temperature as well as several simulation chamber experiments at room temperature were performed. A very weak negative temperature dependence was observed at T ≤ 285 K, and only through the combination of precise data and a large temperature range were we able to discern the transition toward positive temperature dependence found at T ≥ 295 K. The non-Arrhenius temperature dependence of OH + 1,2-epoxybutane implies the agency of prereactive complexes in this reaction mechanism, albeit with a smaller effect than that with its acyclic ether analogues. This will have implications for understanding the chemical fate of epoxides within oxidizing environments.

Section: Experimental Methodsmentioning

confidence: 99%

Gas-Phase Rate Coefficient of OH + 1,2-Epoxybutane Determined between 220 and 950 K

Othmani

Ren

et al. 2021

ACS Earth Space Chem.

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“…The observed independence of the experimental results of the reaction time, which was varied from 0.015 to 0.06 s, seems to support this assumption. It can also be noted that the possible secondary chemistry initiated by oxygen atoms formed in the self-reaction of OH radicals has limited impact on the concentrations of HAC and n -heptane because O atoms are mainly consumed in the fast reactions with OH radicals and NO 2 present in high concentrations in the reactor k 6 = 9.85 × 10 –16 T 1.41 exp (543/ T ) cm 3 molecule –1 s –1 ( T = 220–950 K) k 7 = 1.8 × 10 –11 exp (180/ T ) cm 3 molecule –1 s –1 ( T = 136–515 K) …”

Section: Resultsmentioning

confidence: 99%

Temperature-Dependent Kinetic Study of the Reaction of Hydroxyl Radicals with Hydroxyacetone

2020

J. Phys. Chem. A

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The kinetics of the reaction of OH radicals with hydroxyacetone has been investigated as a function of temperature at (2.0-2.1) Torr total pressure of helium and over an extended temperature range, T = 250-830 K, and as a function of pressure at T = 301 K in the pressure range 1.0-10.4 Torr. The rate constant of the reaction OH + CH 3 C(O)CH 2 OH  products (1) was measured using both absolute (from the kinetics of OH consumption in excess of hydroxyacetone) and relative rate method, k 1 = 4.7×10-22 ×T 3.25 exp(1410/T) cm 3 molecule-1 s-1 at T = 250-830 K. The present data combined with selected previous temperature dependent studies of reaction (1) yield k 1 = 4.4×10-20 ×T 2.63 exp(1110/T) cm 3 molecule-1 s-1 , which is recommended from the present work at T = 230-830K (with conservative uncertainty of 20% at all temperatures). k 1 was found to be pressure independent in the pressure range from 1.0 to 10.4 Torr of He at T = 301 K. The present results are compared with previous experimental and theoretical data.

“…Experiments have been carried out in a discharge-flow apparatus at a total pressure of 2 Torr of helium using electron-impact ionization (25–30 eV energy) mass spectrometry to measure the concentrations of the species involved. − The flow reactor used at low temperatures, T = 220–320 K, consisted of a halocarbon wax-coated Pyrex tube (45 cm length and 2.4 cm i.d.) (Figure S1, Supporting Information).…”

Section: Methodsmentioning

confidence: 99%

“…In the first one, the O concentrations were determined from the decrease in the O 2 concentration upon initiation of the microwave discharge (Δ[O 2 ] = 2[O]). In another method, oxygen atoms were titrated with an excess of NO 2 and their absolute concentrations could be determined from the consumed fraction of NO 2 : [O] = Δ[NO 2 ]. Finally, the absolute concentrations of oxygen atoms could also be determined using their titration by C 2 H 4 S ([O] = [SO] = Δ[C 2 H 4 S]) …”

Section: Methodsmentioning

confidence: 99%

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

2022

ACS Earth Space Chem.

The 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: k 1 = (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: k 1a/k 1 = (0.935 ± 0.005) × exp(−(7.4 ± 0.2)/T) and k 1b/k 1 = (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.