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%.

Experimental and Theoretical Study of the Kinetics of the CH3 + HBr → CH4 + Br Reaction and the Temperature Dependence of the Activation Energy of CH4 + Br → CH3 + HBr.

The rate coefficient of the reaction of CH3 with HBr was measured and calculated in the temperature range 225-960 K. The results of the measurements performed in a flow apparatus with mass spectrometric detection agree very well with the quasiclassical trajectory calculations performed on a previously developed potential energy surface. The experimental rate coefficients are described well with a double-exponential fit, k1(exp) = [1.44 × 10-12 exp(219/T) + 6.18 × 10-11 exp(-3730/T)] cm3 molecule-1 s-1. The individual rate coefficients below 500 K accord with the available experimental data as does the slightly negative activation energy in this temperature range, -1.82 kJ/mol. At higher temperatures, the activation energy was found to switch sign and it rises up to about an order of magnitude larger positive value than that below 500 K, and the rate coefficient is about 50% larger at 960 K than that around room temperature. The rate coefficients calculated with the quasiclassical trajectory method display the same tendencies and are within about 8% of the experimental data between 960 and 300 K and within 25% below that temperature. The significant variation of the magnitude of the activation energy can be reconciled with the tabulated heats of formation only if the activation energy of the reverse CH4 + Br reaction also significantly increases with the temperature.

Rate Coefficients of the Reactions of Fluorine Atoms with H2S and SH over the Temperature Range 220-960 K.

Reaction F + H2S→SH + HF (1) is an effective source of SH radicals and an important intermediate in atmospheric and combustion chemistry. We employed a discharge-flow, modulated molecular beam mass spectrometry technique to determine the rate coefficient of this reaction and that of the secondary one, F + SH→S + HF (2), at a total pressure of 2 Torr and in a wide temperature range 220-960 K. The rate coefficient of Reaction (1) was determined directly by monitoring consumption of F atoms under pseudo-first-order conditions in an excess of H2S. The rate coefficient of Reaction (2) was determined via monitoring the maximum concentration of the product of Reaction (1), SH radical, as a function of [H2S]. Both rate coefficients were found to be virtually independent of temperature in the entire temperature range of the study: k1 = (1.86 ± 0.28) × 10-10 and k2 = (2.0 ± 0.40) × 10-10 cm3 molecule-1 s-1. The kinetic data from the present study are compared with previous room temperature measurements.

OH Radical and Chlorine Atom Kinetics of Substituted Aromatic Compounds: 4-chlorobenzotrifluoride (p-ClC6H4CF3).

The mechanisms for the OH radical and Cl atom gas-phase reaction kinetics of substituted aromatic compounds remain a topic of atmospheric and combustion chemistry research. 4-Chlorobenzotrifluoride (p-chlorobenzotrifluoride, p-ClC6H4CF3, PCBTF) is a commonly used substituted aromatic volatile organic compound (VOC) in solvent-based coatings. As such, PCBTF is classified as a volatile chemical product (VCP) whose release into the atmosphere potentially impacts air quality. In this study, rate coefficients, k1, for the OH + PCBTF reaction were measured over the temperature ranges 275-340 and 385-940 K using low-pressure discharge flow-tube reactors coupled with a mass spectrometer detector in the ICARE/CNRS (Orléans, France) laboratory. k1(298-353 K) was also measured using a relative rate method in the thermally regulated atmospheric simulation chamber (THALAMOS; Douai, France). k1(T) displayed a non-Arrhenius temperature dependence with a negative temperature dependence between 275 and 385 K given by k1(275-385 K) = (1.50 ± 0.15) × 10-14 exp((705 ± 30)/T) cm3 molecule-1 s-1, where k1(298 K) = (1.63 ± 0.03) × 10-13 cm3 molecule-1 s-1 and a positive temperature dependence at elevated temperatures given by k1(470-950 K) = (5.42 ± 0.40) × 10-12 exp(-(2507 ± 45) /T) cm3 molecule-1 s-1. The present k1(298 K) results are in reasonable agreement with two previous 296 K (760 Torr, syn. air) relative rate measurements. The rate coefficient for the Cl-atom + PCBTF reaction, k2, was also measured in THALAMOS using a relative rate technique that yielded k2(298 K) = (7.8 ± 2) × 10-16 cm3 molecule-1 s-1. As part of this work, the UV and infrared absorption spectra of PCBTF were measured (NOAA; Boulder, CO, USA). On the basis of the UV absorption spectrum, the atmospheric instantaneous UV photolysis lifetime of PCBTF (ground level, midlatitude, Summer) was estimated to be 3-4 days, assuming a unit photolysis quantum yield. The non-Arrhenius behavior of the OH + PCBTF reaction over the temperature range 275 to 950 K is interpreted using a mechanism for the formation of an OH-PCBTF adduct and its thermochemical stability. The results from this study are included in a discussion of the OH radical and Cl atom kinetics of halogen substituted aromatic compounds for which only limited temperature-dependent kinetic data are available.

Experimental Study of the Reaction of O(3P) with Carbonyl Sulfide between 220 and 960 K.

The reaction of a ground-state O atom with carbonyl sulfide is of interest for atmospheric (stratosphere and hot near-source volcanic plume) and combustion chemistry. In the present work, we employed a discharge-flow system combined with a modulated molecular beam mass spectrometry technique to measure the rate constant and products of the O + OCS reaction. The overall rate constant was determined either from the kinetics of the reaction product, SO radical, formation or under pseudo-first-order conditions from the decays of OCS in an excess of oxygen atoms: k1 = 1.92 × 10-12 × (T/298)2.08 exp(-1524/T) cm3 molecule-1 s-1 at T = 220-960 K, with conservative uncertainty of 20%. The yield of another reaction product, CO2, was found to increase from 3.55% at T = 455 K to 14.2% at T = 960 K, resulting in the following Arrhenius expression for the rate constant of the minor (S + CO2 forming) reaction channel: k1b = 4.19 × 10-11 exp(-4088/T) cm3 molecule-1 s-1 at T = 455-960 K (with an uncertainty of 25%). The kinetic and mechanistic data from the present work are discussed in comparison with previous experimental and computational studies.

Reaction Rate Coefficient of OH Radicals with d 9-Butanol as a Function of Temperature.

d 9-Butanol or 1-butan-d 9-ol (D9B) is often used as an OH radical tracer in atmospheric chemistry studies to determine OH exposure, a useful universal metric that describes the extent of OH radical oxidation chemistry. Despite its frequent application, there is only one study that reports the rate coefficient of D9B with OH radicals, k 1(295 K), which limits its usefulness as an OH tracer for studying processes at temperatures lower or higher than room temperature. In this study, two complementary experimental techniques were used to measure the rate coefficient of D9B with OH radicals, k 1(T), at temperatures between 240 and 750 K and at pressures within 2-760 Torr. A thermally regulated atmospheric simulation chamber was used to determine k 1(T) in the temperature range of 263-353 K and at atmospheric pressure using the relative rate method. A low-pressure (2-10 Torr) discharge flow tube reactor coupled with a mass spectrometer was used to measure k 1(T) at temperatures within 240-750 K, using both the absolute and relative rate methods. The agreement between the two experimental aproaches followed in this study was very good, within 6%, in the overlapping temperature range, and k 1(295 ± 3 K) was 3.42 ± 0.26 × 10-12 cm3 molecule-1 s-1, where the quoted error is the overall uncertainty of the measurements. The temperature dependence of the rate coefficient is well described by the modified Arrhenius expression, k 1 = (1.57 ± 0.88) × 10-14 × (T/293)4.60±0.4 × exp(1606 ± 164/T) cm3 molecule-1 s-1 in the range of 240-750 K, where the quoted error represents the 2σ standard deviation of the fit. The results of the current study enable an accurate estimation of OH exposure in atmospheric simulation experiments and expand the applicability of D9B as an OH radical tracer at temperatures other than room temperature.

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

The 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.

Disproportionation Channel of the Self-reaction of Hydroxyl Radical, OH + OH → H2O + O, Revisited.

The rate constant of the disproportionation channel 1a of the self-reaction of hydroxyl radicals OH + OH → H2O + O (1a) was measured at ambient temperature as well as over an extended temperature range to resolve the discrepancy between the IUPAC recommended value (k1a = 1.48 × 10-12 cm3 molecule-1 s-1, discharge flow system, Bedjanian et al. J. Phys. Chem. A 1999, 103, 7017) and a factor of ca. 1.8 higher value by pulsed laser photolysis (2.7 × 10-12 cm3 molecule-1 s-1, Bahng et al. J. Phys. Chem. A 2007, 111, 3850, and 2.52 × 10-12 cm3 molecule-1 s-1, Altinay et al. J. Phys. Chem. A 2014, 118, 38). To resolve this discrepancy, the rate constant of the title reaction was remeasured in three laboratories using two different experimental techniques, namely, laser-pulsed photolysis-transient UV absorption and fast discharge flow system coupled with mass spectrometry. Two different precursors were used to generate OH radicals in the laser-pulsed photolysis experiments. The experiments confirmed the low value of the rate constant at ambient temperature (k1a = (1.4 ± 0.2) × 10-12 cm3 molecule-1 s-1 at 295 K) as well as the V-shaped temperature dependence, negative at low temperatures and positive at high temperatures, with a turning point at 427 K: k1a = 8.38 × 10-14 × (T/300)1.99 × exp(855/T) cm3 molecule-1 s-1 (220-950 K). Recommended expression over the 220-2384 K temperature range: k1a = 2.68 × 10-14 × (T/300)2.75 × exp(1165/T) cm3 molecule-1 s-1 (220-2384 K).

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

The kinetics of the reaction of OH radicals with hydroxyacetone has been investigated as a function of temperature at a total pressure of helium of 2.0-2.1 Torr and over an extended temperature range of 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 + CH3C(O)CH2OH → products (1) was measured using both absolute (from the kinetics of OH consumption in excess of hydroxyacetone) and relative rate methods (k1 = 4.7 × 10-22 × T3.25 exp (1410/T) cm3 molecule-1 s-1 at T = 250-830 K). The present data combined with selected previous temperature-dependent studies of reaction (1) yield k1 = 4.4 × 10-20 × T2.63 exp (1110/T) cm3 molecule-1 s-1, which is recommended from the present work at T = 230-830 K (with conservative uncertainty of 20% at all temperatures). k1 was found to be independent of the pressure in the 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.

Temperature-Dependent Rate Constant for the Reaction of Hydroxyl Radical with 3-Hydroxy-3-methyl-2-butanone.

Reactions of hydroxyketones with OH radicals are of importance in atmospheric chemistry and represent a theoretical interest because they proceed through two reaction pathways, formation of a hydrogen-bonded prereactive complex and direct H-atom abstraction. In this work, the kinetics of the reaction of OH radicals with 3-hydroxy-3-methyl-2-butanone (3H3M2B) has been investigated at 2 Torr total pressure of helium over a wide temperature range, T = 278-830 K, using a discharge flow reactor combined with an electron impact ionization quadrupole mass spectrometer. The rate constant of the reaction OH + 3H3M2B → products (1) was determined using both a relative rate method and absolute measurements under pseudo-first-order conditions, monitoring the kinetics of OH consumption in excess of 3H3M2B, k1= 5.44 × 10-41T9.7exp (2820/T) and 1.23 × 10-11 exp (-970/T) cm3 molecule-1 s-1 at T = 278-400 and 400-830 K, respectively (with a total uncertainty of 20% at all temperatures). The rate constant of the reaction OH + Br2 → HOBr + Br (2) was measured as a part of this study using both absolute and relative rate methods: k2 = 2.16 × 10-11 exp (207/T) cm3 molecule-1 s-1 at T = 220-950 K (with conservative 10% uncertainty). The kinetic data from the present study are discussed in comparison with previous measurements and theoretical calculations.

Reaction F + C2H4: Rate Constant and Yields of the Reaction Products as a Function of Temperature over 298-950 K.

The kinetics and products of the reaction of F + C2H4 have been studied in a discharge flow reactor combined with an electron impact ionization mass spectrometer at nearly 2 Torr total pressure of helium in the temperature range 298-950 K. The total rate constant of the reaction, k1 = (1.78 ± 0.30) × 10-10 cm3 molecule-1 s-1, determined under pseudo-first-order conditions, monitoring the kinetics of F atom consumption in excess of C2H4, was found to be temperature independent in the temperature range used. H, C2H3F, and HF were identified as the reaction products. Absolute measurements of the yields of these species allowed to determine the branching ratios, k1b/ k1 = (0.73 ± 0.07) exp(-(425 ± 45)/ T) and k1a/ k1 = 1 - (0.73 ± 0.07) exp(-(425 ± 45)/ T) and partial rate constants for addition-elimination (H + C2H3F) and H atom abstraction (HF + C2H3) pathways of the title reaction: k1a = (0.80 ± 0.07) × 10-10exp(189 ± 37/ T) and k1b = (1.26 ± 0.13) × 10-10exp(-414 ± 45/ T) cm3 molecule-1 s-1, respectively, at T = 298-950 K and with 2σ quoted uncertainties. The overall reaction rate constant can be adequately described by both the temperature independent value and as a sum of k1a and k1b. The kinetic and mechanistic data from the present study are discussed in comparison with previous absolute and relative measurements and theoretical calculations.

Kinetics and Products of the Reaction of OH Radicals with ClNO from 220 to 940 K.

The kinetics and products of the reaction of OH radicals with ClNO have been studied in a flow reactor coupled with an electron impact ionization mass spectrometer at nearly 2 Torr total pressure of helium and over a wide temperature range, T = 220-940 K. The rate constant of the reaction OH + ClNO → products was determined under pseudo-first order conditions, monitoring the kinetics of OH consumption in excess of ClNO: k1 = 1.48 × 10-18 × T2.12 exp(146/T) cm3 molecule-1 s-1 (uncertainty of 15%). HOCl, Cl, and HONO were observed as the reaction products. As a result of quantitative detection of HOCl and Cl, the partial rate constants of the HOCl + NO and Cl + HONO forming reaction pathways were determined in the temperature range 220-940 K: k1a = 3.64 × 10-18 × T1.99 exp(-114/T) and k1b = 4.71 × 10-18 × T1.74 exp(246/T) cm3 molecule-1 s-1 (uncertainty of 20%). The dynamics of the title reaction and, in particular, non-Arrhenius behavior observed for both k1a and k1b in a wide temperature range, seems to be an interesting topic for theoretical research.

Kinetics and Products of the Reactions of Fluorine Atoms with ClNO and Br2 from 295 to 950 K.

The kinetics and products of the reactions of F atoms with Br2 and ClNO have been studied in a flow reactor coupled with an electron impact ionization mass spectrometer at nearly 2 Torr total pressure of helium and over a wide temperature range, T = 295-950 K. The rate constant of the reaction F + ClNO → products (1) was determined under pseudo-first order conditions, monitoring the kinetics of F atom consumption in excess of ClNO. The measured temperature independent rate constant, k1 = (1.29 ± 0.13) × 10-10 cm3 molecule-1 s-1 (T = 299-950 K), was found to be in excellent agreement with the only previous low temperature study which allowed to recommend the value of k1 in an extended temperature range, 228-950 K. FCl and Cl atoms were observed as the reactions products (corresponding to two reaction pathways: Cl-atom abstraction and replacement with fluorine atom, respectively) with the independent of temperature, in the range 295-948 K, yields of 0.68 ± 0.10 and 0.32 ± 0.05, respectively. Rate constant of the reaction F + Br2 (2), k2 = (1.28 ± 0.20) × 10-10 cm3 molecule-1 s-1, determined using both absolute and relative rate methods, was found to be independent of temperature at T = 299-940 K.

Reaction of O(3P) with C3H6: Yield of the Reaction Products as a Function of Temperature.

Reaction of oxygen atoms with propene is an important step in combustion processes particularly affecting the profiles of intermediate species and flame speed. The relative importance of different pathways of this multichannel reaction at different temperatures represents significant theoretical interest and is essential for modeling combustion systems. In the present work, we report the first experimental investigation of the products of the O(3P) + C3H6 reaction over an extended temperature range (298-905 K). By using a low pressure flow reactor combined with a quadrupole mass spectrometer, the yields of the five reaction products, H atom, CH3, C2H5, CH2O and OH were determined as a function of temperature between 298 and 905 K: 0.0064 × (T/298)2.74 exp(765/T), 1.41 × (T/298)-1.0 exp(-335/T), 0.92 × (T/298)-1.41 exp(-381/T), 0.17 × (T/298)0.165 exp(-36/T), and 0.0034 × (T/298)2.34 exp(788/T), respectively (corresponding to the variation of the respective yields between 298 and 905 K in the ranges 0.08-0.31, 0.46-0.32, 0.26-0.12, 0.15-0.19, and 0.05-011), independent of pressure in the range 1-8 Torr of helium. For the yields of the minor reaction products, H2 and CH3CHO the upper limits were determined as 0.2 and 0.05, respectively. These results are compared with the experimental data and theoretical calculations available in the literature.

Atmospheric Chemistry of 1-Methoxy 2-Propyl Acetate: UV Absorption Cross Sections, Rate Coefficients, and Products of Its Reactions with OH Radicals and Cl Atoms.

The rate coefficients for the reactions of OH and Cl with 1-methoxy 2-propyl acetate (MPA) in the gas phase were measured using absolute and relative methods. The kinetic study on the OH reaction was conducted in the temperature (263-373) K and pressure (1-760) Torr ranges using the pulsed laser photolysis-laser-induced fluorescence technique, a low pressure fast flow tube reactor-quadrupole mass spectrometer, and an atmospheric simulation chamber/GC-FID. The derived Arrhenius expression is kMPA+OH(T) = (2.01 ± 0.02) × 10-12 exp[(588 ± 123/T)] cm3 molecule-1 s-1. The absolute and relative rate coefficients for the reaction of Cl with MPA were measured at room temperature in the flow reactor and the atmospheric simulation chamber, which led to k(Cl+MPA) = (1.98 ± 0.31) × 10-10 cm3 molecule-1 s-1. GC-FID, GC-MS, and FT-IR techniques were used to investigate the reaction mechanism in the presence of NO. The products formed from the reaction of MPA with OH and their yields were methyl formate (80 ± 7.3%), acetic acid (50 ± 4.8%), and acetic anhydride (22 ± 2.4%), while for Cl reaction, the obtained yields were 60 ± 5.4, 41 ± 3.8, and 11 ± 1.2%, respectively, for the same products. The UV absorption cross section spectrum of MPA was determined in the wavelength range 210-370 nm. The study has shown no photolysis of MPA under atmospheric conditions. The obtained results are used to derive the atmospheric implication.

Reaction of O(3P) with C2H4: Yield of the Reaction Products as a Function of Temperature.

Reaction of oxygen atoms with ethylene is an important step in the combustion process particularly affecting the profiles of intermediate species and flame speed. Currently, the relative importance of different pathways of this multichannel reaction at different temperatures is not fully established and determination of the branching ratios for different reaction channels as a function of temperature remains essential for modeling combustion systems. In the present work, the products of the O(3P) + C2H4 reaction have been studied over an extended temperature range (297-900 K) using a low pressure flow reactor (1-8 Torr) combined with a quadrupole mass spectrometer. The yields of the three main reaction products, H atom, CH3 radical, and CH2O, were determined to be 0.31 ± 0.05, 0.53 ± 0.09, and 0.17 ± 0.03, respectively, independent of pressure and temperature under experimental conditions of the study. For the yields of the minor reaction products, H2 and CH4, the upper limits were determined as 0.05 and 0.02, respectively. These results are compared with the experimental data and theoretical calculations available in the literature.

Thermal Decomposition of Isopropyl Nitrate: Kinetics and Products.

Kinetics and products of the thermal decomposition of isopropyl nitrate (IPN, C3H7NO3) have been studied using a low pressure flow reactor combined with a quadrupole mass spectrometer. The rate constant of IPN decomposition was measured as a function of pressure (1-12.5 Torr of helium) and temperature in the range 473-658 K using two methods: from kinetics of nitrate loss and those of reaction product (CH3 radical) formation. The fit of the observed falloff curves with two parameter expression [Formula: see text] provided the following low and high pressure limits for the rate constant of IPN decomposition: k0 = 6.60 × 10-5exp(-15190/T) cm3 molecule-1 s-1 and k∞ = 1.05 × 1016 exp(-19850/T) s-1, respectively, which allows one to determine (via the above expression) the values of k1 (with 20% uncertainty) in the temperature and pressure range of the study. It was observed that thermal decomposition of IPN proceeds through initial breaking of the O-NO2 bond, leading to formation of NO2 and isopropoxy radical (CH3)2CHO, which rapidly decomposes forming CH3 and acetaldehyde as final products. The yields of NO2, CH3, and acetaldehyde upon decomposition of isopropyl nitrate were measured to be (0.98 ± 0.15), (0.96 ± 0.14), and (0.99 ± 0.15), respectively. In addition, the kinetic data were used to determine the O-NO2 bond dissociation energy in isopropyl nitrate, 38.2 ± 4.0 kcal mol-1.

Gas-Phase Reaction of Hydroxyl Radical with p-Cymene over an Extended Temperature Range.

The kinetics of the reaction of OH radicals with p-cymene has been studied in the temperature range of 243-898 K using a flow reactor combined with a quadrupole mass spectrometer: OH + p-cymene → products. The reaction rate constant was determined as a result of absolute measurements, from OH decay kinetics in excess of p-cymene and employing the relative rate method with OH reactions with n-pentane, n-heptane,1,3-dioxane, HBr, and Br2 as the reference ones. For the rate coefficient of the H atom abstraction channel, the expression k1b = (3.70 ± 0.42) × 10(-11) exp[-(772 ± 72)/T] was obtained over the temperature range of 381-898 K. The total rate constant (addition + abstraction) determined at T = 243-320 K was k1 = (1.82 ± 0.48) × 10(-12) exp[(607 ± 70)/T] or, in a biexponential form, k1 = k1a + k1b = 3.7 × 10(-11) exp(-772/T) + 6.3 × 10(-13) exp(856/T), independent of the pressure between 1 and 5 Torr of helium. In addition, our results indicate that the reaction pathway involving alkyl radical elimination upon initial addition of OH to p-cymene is most probably unimportant.

Investigation of the photochemical reactivity of soot particles derived from biofuels toward NO2. A kinetic and product study.

In the current study, the heterogeneous reaction of NO2 with soot and biosoot surfaces was investigated in the dark and under illumination relevant to atmospheric conditions (J(NO2) = 0.012 s(-1)). A flat-flame burner was used for preparation and collection of soot samples from premixed flames of liquid fuels. The biofuels were prepared by mixing 20% v/v of (i) 1-butanol (CH3(CH2)3OH), (ii) methyl octanoate (CH3(CH2)6COOCH3), (iii) anhydrous diethyl carbonate (C2H5O)2CO and (iv) 2,5 dimethyl furan (CH3)2C4H2O additive compounds in conventional kerosene fuel (JetA-1). Experiments were performed at 293 K using a low-pressure flow tube reactor (P = 9 Torr) coupled to a quadrupole mass spectrometer. The initial and steady-state uptake coefficients, γ0 and γ(ss), respectively, as well as the surface coverage, N(s), were measured under dry and humid conditions. Furthermore, the branching ratios of the gas-phase products NO (∼80-100%) and HONO (<20%) were determined. Soot from JetA-1/2,5-dimethyl furan was the most reactive [γ0 = (29.1 ± 5.8) × 10(-6), γ(ss)(dry) = (9.09 ± 1.82) × 10(-7) and γ(ss)(5.5%RH) = (14.0 ± 2.8)(-7)] while soot from JetA-1/1-butanol [γ0 = (2.72 ± 0.544) × 10(-6), γ(ss)(dry) = (4.57 ± 0.914) × 10(-7), and γ(ss)(5.5%RH) = (3.64 ± 0.728) × 10(-7)] and JetA-1/diethyl carbonate [γ0 = (2.99 ± 0.598) × 10(-6), γ(ss)(dry) = (3.99 ± 0.798) × 10(-7), and γ(ss)(5.5%RH) = (4.80 ± 0.960) × 10(-7)] were less reactive. To correlate the chemical reactivity with the physicochemical properties of the soot samples, their chemical composition was analyzed employing Raman spectroscopy, NMR, and high-performance liquid chromatography. In addition, the Brunauer-Emmett-Teller adsorption isotherms and the particle size distributions were determined employing a Quantachrome Nova 2200e gas sorption analyzer. The analysis of the results showed that factors such as (i) soot mass collection rate, (ii) porosity of the particles formed, (iii) aromatic fraction, and (iv) pre-existence of nitro-containing species in soot samples (formed during the combustion process) can be used as indicators of soot reactivity with NO2.

Reaction of limonene with F2: rate coefficient and products.

The kinetics of the reaction of limonene (C10H16) with F2 has been studied using a low pressure (P = 1 Torr) and a high pressure turbulent (P = 100 Torr) flow reactor coupled with an electron impact ionization and chemical ionization mass spectrometers, respectively: F2 + Limonene → products (1). The rate constant of the title reaction was determined under pseudo-first-order conditions by monitoring either limonene or F2 decay in excess of F2 or C10H16, respectively. The reaction rate constant, k1 = (1.15 ± 0.25) × 10(-12) exp(160 ± 70)/T) was determined over the temperature range 278-360 K, independent of pressure between 1 (He) and 100 (N2) Torr. F atom and HF were found to be formed in reaction 1 , with the yields of 0.60 ± 0.13 and 0.39 ± 0.09, respectively, independent of temperature in the range 296-355 K.