Relative Rate Coefficients Research Articles

Kinetics, products and mechanisms of the OH radicals and Cl atoms reactions with trans-2-octene and cycloheptene

Relative rate coefficients for the gas-phase reactions of OH radicals and Cl atoms with trans-2-octene (k1-OH and k2-Cl) and cycloheptene (k3-OH and k4-Cl) have been determined by in situ Fourier Transform Infrared Spectroscopy (FTIR). The experiments were carried out at 298 ± 2 K and atmospheric pressure (760 ± 10) Torr using synthetic air as bath gas. The following rate coefficients (in units of cm3 molecule−1 s−1) were obtained for the reactions of trans-2-octene and cycloheptene with OH radicals and Cl atoms: k1-OH = (8.51 ± 1.86) × 10−11, k2-Cl = (4.47 ± 1.09) × 10−10, k3-OH = (7.84 ± 1.78) × 10−11, k4-Cl = (5.46 ± 1.01) × 10−10, respectively. This is the first kinetic study for the reactions of trans-2-octene with Cl atoms and the first rate coefficient determination for the title reactions by in situ FTIR spectroscopy. The kinetic data were compared with previously reported values for similar compounds and reactivity trends were developed. Complementary, products identification studies were performed in similar conditions to the kinetic experiments by the in situ FTIR and Gas Chromatography coupled to mass spectrometry (GC-MS). The atmospheric chemical mechanisms were postulated for the first time for both unsaturated compounds. In addition, the atmospheric implications of these reactions were assessed through the estimation of the tropospheric lifetimes, Photochemical Ozone Creation Potential (POCP) and fates of these compounds in the troposphere.

Kinetics of the reaction of OH radical with ethylfluoroacetate, ethyl 4,4,4-trifluorobutyrate, and butylfluoroacetate

Kinetics of the gas-phase reactions of •OH radicals with a series of fluoroesters were studied for the first time at 298 ± 3 K and atmospheric pressure. Relative rate coefficients were determined by in situ FTIR spectroscopy in nitrogen and GC-FID in air to monitor the decay of reactants and references. The following coefficient values (in 10−12 cm3/(molecule•sec)) were obtained for ethyl fluoroacetate (EFA), ethyl 4,4,4-trifluorobutyrate (ETB), and butyl fluoroacetate (BFA), respectively: k1 (EFA + OH) = 1.15 ± 0.25 by FTIR and 1.34 ± 0.23 by GC-FID; k2 (ETB + OH) = 1.61 ± 0.36 by FTIR and 2.02 ± 0.30 by GC-FID; k3 (BFA + OH) = 2.24 ± 0.37 by FTIR. Reactivity trends were developed and correlated with the number of CH3 and F substituents in the fluoroester, and structure-activity relationships (SARs) calculations were performed. In addition, the tropospheric lifetimes of EFA, ETB, and BFA upon degradation by OH radicals were calculated to be 9, 6, and 5 days, respectively, indicating that these fluorinated compounds could have a possible regional effect from the emission source. Relatively small photochemical ozone creation potentials of 9, 7, and 19 were estimated for EFA, ETB, and BFA, respectively. The Global Warming Potentials (GWPs) for EFA, ETB, and BFA were calculated for different time horizons. For a 20-year time horizon, the GWPs were 1.393, 0.063, and 0.062, respectively. In the case of a 100-year time horizon, the GWPs were 0.379, 0.017, and 0.017, and for a 500-year time horizon, the GWPs were 0.108, 0.005, and 0.005 for EFA, ETB, and BFA.

Use of Azolla Plant in Broiler Diets and its Effect on Productive Performance

This study was conducted in the poultry farm, the Department of the Animal Production / University of Mosul. The aim was to partially replace Azolla in the diet of broiler chickens as a nutritional management method to include it as an available local feed ingredient and to study its effect on productive traits, economic implications and carcass traits. The duration of experiment lasted 42 days, and the experiment included four treatments by adding different percentages of dried Azolla with three replicates for each treatment: T1 (control): a diet free of Azolla T2: a diet containing dried Azolla at a rate of 4.5%. T3: a diet containing dried Azolla at a rate of 9%. T4: a diet containing 13.5% of dried Azolla. The results of the statistical analysis were: There were no significant differences (p ≤ 0.05) between the treatments of Azolla added to the diet compared with the control in the average live body weight, weight gain, relative growth rate, feed consumption and feed conversion coefficient, and increase in the value of economic indicators, coefficient, production index and productivity yield kg/ m2 With a significant decrease in the percentage of total mortality for a period of five and six weeks.

Hydroxy esters atmospheric degradation: OH and Cl reactivity, products distribution and fate of the alkoxy radicals formed

Kinetic studies of the reaction of ethyl glycolate HOCH2C(O)OCH2CH3 with OH radicals (kOH) and Cl atoms (kCl) have been conducted by the relative method using a glass atmospheric reactor by “in situ” Fourier Transform Infrared (FTIR) and Gas Chromatography equipped with flame ionization detection by Solid Phase Micro Extraction (GC-FID/SPME) at room temperature and atmospheric pressure. The following relative rate coefficients were determined using several reference compounds and two different techniques: kEG + OH-FTIR = (4.36 ± 1.21) × 10−12; kEG + OH-GC-FID= (3.90 ± 0.74) × 10−12; and kEG + Cl-GC-FID= (6.40 ± 0.72) × 10−11 all values in units of cm3.molecule−1.s−1. Complementary product studies were performed under comparable conditions to the kinetic tests, in order to identify the reaction products and to postulate their tropospheric oxidation mechanisms. The reaction of OH radicals and Cl atoms with ethyl glycolate initiates via H-atom abstraction from alkyl groups of the molecule. Formic acid was positively identified as a reaction product by FTIR. On the other hand, formaldehyde, acetaldehyde, glycolic acid; and formic acid were identified by the GC-MS technique. The Structure–Activity Relationship, (SAR) calculations were also implemented to estimate the more favorable reaction pathways and compare them with the products identified. Tropospheric lifetimes of τOH = 34 h and τCl = 5.5 days were estimated to determine how these investigated reactions might affect the air quality. In this sense, average ozone production of [O3] = 0.75 and a Photochemical Ozone Creation Potential, POCP, of 38 were calculated for the hydroxyl ester studied.

Investigation of dietary exogenous protease and humic substance on growth, disease resistance to Flavobacterium covae and immune responses in juvenile channel catfish (Ictalurus punctatus).

Many bacterial pathogens impact the US catfish industry, and disease control can be challenging for producers. Columnaris disease in channel catfish, Ictalurus punctatus, is primarily caused by Flavobacterium covae (formerly F. columnare). Immunostimulants may enhance nonspecific immune responses and offer an alternative to antibiotic treatments in catfish. Furthermore, dietary protein sources and inclusions are also essential to fish health and nutrition and may enhance overall fish performance in pond culture. The current project evaluated two immunostimulants: a protease complex (PC) and a humic substance (HS) derived from a reed-sedge peat product. A 60-day trial examined the effects of five diets on growth performance, immune response and resistance to experimental F. covae infection in channel catfish. Diets included a high-quality fishmeal diet (32%; CF32), a high-protein soy-based diet (32%; C32), a low-protein soy-based diet (28%; C28; predominately used in industry), a low-protein soy diet supplemented with C28 + PC at 175 g metric ton-1 and C28 + HS in a low-protein diet at 23 g metric ton-1 . Following feeding for 60 d, juvenile channel catfish were sampled for growth performance and baseline health indicators (n = 3; body mucus, blood for sera, kidney and spleen). A subset of fish was then subjected to an immersion-based in vivo challenge trial with F. covae (ALG-00-530; 106 CFU mL-1 exposure). At 60d post-initiation, there were no dietary differences in the relative growth rate (p = .063) or thermal growth coefficient (p = .055), but the 32% diets generally appeared to perform best. Post-challenge, the C32 group's mortality was higher than the C28 + PC (p = .006) and C28 + HS diets (p = .005). Although not significant, the C28 and CF32 groups also demonstrated higher mortality compared to both PC and HS diets. Sera lysozyme concentration was found to increase following pathogen challenge (p < .001) and in comparison with mock-challenged catfish (p < .001). Elevated expression levels of proinflammatory cytokines (il-1β, il-8, tnf-α and tgf-β) were observed at trial midpoint and post-infection when compared to 60d. The C28 treatment was found to have lower tnf-α expression than the C28 + PC (p = .042) and C28 + HS (p = .042) groups following exposure to F. covae. These challenge data suggest that the immunostimulants (PC and HS) in plant-based protein may be beneficial in protecting against F. covae when offered in low-protein channel catfish diets.

Atmospheric degradation of chloroacetoacetates by Cl atoms: Reactivity, products and mechanism in coastal and industrialized areas

Kinetic studies of the reaction of Cl atoms with ethyl 2-chloroacetoacetate, CH3C(O)CHClC(O)OCH2CH3, (k1) and methyl 2-chloroacetoacetate, CH3C(O)CHClC(O)OCH3, (k2) have been developed for the first time using SPME/GC-FID and in situ FTIR spectroscopy at (298 ± 2) K and 1000 mbar in glass atmospheric chambers. Relative rate coefficients obtained by Fourier Transform Infrared Spectroscopy (FTIR) using different reference compounds, were the following (in cm3.molecule−1.s−1): kE2CAA-FTIR= (2.41 ± 0.57) × 10−10 and kM2CAA-FTIR= (2.16 ± 0.85) × 10−10. Similar and reproducible values were obtained using Gas Chromatography equipped with Flame Ionization Detection coupled with Solid Phase Micro Extraction (SPME), kE2CAA-GC-FID = (2.54 ± 0.81) × 10−10 and kM2CAA-GC-FID = (2.34 ± 0.87) × 10−10 all values in units of cm3.molecule−1.s−1. In addition, product studies were performed in similar conditions to the kinetic experiments to identify the reaction products and postulate their tropospheric degradation mechanisms. The reaction of Cl atoms with saturated esters initiates via H-atom abstraction from the alkyl groups of the molecule. Formyl chloride, chloroacetone, and acetyl chloride were positively identified as reaction products by FTIR. On the other hand, acetyl chloride, 1,1,1-trichloropropan-2-one, 1,1-dichloropropan-2-one, 1-chloropropan-2-one, ethyl chloroformate, and methyl chloroformate were identified by the GC-MS technique. Structure–Activity Relationship (SAR), calculations were also performed to estimate the more favorable reactions pathways in agreement with the products observed. The atmospheric implications of these reactions were assessed by the estimation of the residence times of the chloroesters studied as following: τCl-E2CAA = 1.47 days, and τCl-M2CAA = 1.57 days. Additionally, the possible impact of the emission of chloro acetoacetates in rain acidification was evaluated from the moderate Acidification Potentials (AP), 0.19, and 0.21 obtained for E2CAA and M2CAA, respectively.

Room temperature rate coefficients for the reaction of chlorine atoms with a series of volatile methylsiloxanes (L2‐L5, D3‐D6)

AbstractThe kinetics of chlorine (Cl) atom reactions with a series of volatile methylsiloxanes (VMS) including hexamethyldisiloxane (L2), octamethyltrisiloxane (L3), decamethyltetrasiloxane (L4), dodecamethylpentasiloxane (L5), hexamethylcyclotrisiloxane (D3), octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), and dodecamethylcyclohexasiloxane (D6) were investigated in relative rate experiments at room temperature and atmospheric pressure. The experiments were carried out in a 0.2 m3 PFA Teflon chamber, employing proton‐transfer‐reaction time‐of‐flight mass spectrometry (PTR‐ToF‐MS) as the chemical‐analytical tool. The following relative and absolute reaction rate coefficients were obtained using isoprene as reference compound (kVMS/kisoprene; kVMS × 1010 cm3 molec−1 s −1): L2 (0.32 ± 0.02; 1.31 ± 0.21), L3 (0.38 ± 0.00; 1.56 ± 0.23), L4 (0.48 ± 0.01; 1.98 ± 0.29), L5 (0.54 ± 0.03; 2.22 ± 0.34), D3 (0.14 ± 0.02; 0.56 ± 0.13), D4 (0.26 ± 0.01; 1.05 ± 0.16), D5 (0.36 ± 0.02; 1.46 ± 0.22), D6 (0.39 ± 0.02; 1.61 ± 0.25). The following relative and absolute reaction rate coefficients were obtained using toluene as reference compound (kVMS/ktoluene; kVMS × 1010 cm3 molec−1 s −1): L2 (1.59 ± 0.18; 0.95 ± 0.14), L3 (2.25 ± 0.14; 1.35 ± 0.16), L4 (2.38 ± 0.01; 1.43 ± 0.14), L5 (3.57 ± 0.11; 2.14 ± 0.22), D3 (0.87 ± 0.01; 0.52 ± 0.05), D4 (1.48 ± 0.12; 0.89 ± 0.11), D5 (2.02 ± 0.15; 1.21 ± 0.15), D6 (2.54 ± 0.11; 1.52 ± 0.17). Our data confirm that reactions with Cl atoms need to be taken into account when assessing the decomposition of VMS in Cl‐rich tropospheric environments.

Conformational-Dependent Photodissociation of Glycolic Acid in an Argon Matrix

Ultraviolet-induced photodissociation and photo-isomerization of the three most stable conformers (SSC, GAC, and AAT) of glycolic acid are investigated in a low-temperature solid argon matrix using FTIR spectroscopy and employing laser radiation with wavelengths of 212 nm, 226 nm, and 230 nm. The present work broadens the wavelength range of photochemical studies of glycolic acid, thus extending the understanding of the overall photochemistry of the compound. The proposed kinetic model for the photodissociation of glycolic acid proceeds from the lowest energy conformer (SSC). The model suggests that ultraviolet light induces isomerization only between the SSC and GAC conformers and between the SSC and AAT conformers. The relative reaction rate coefficients are reported for all proposed reactions. These results suggest that the direct photodissociation of GAC and AAT conformer does not occur in an argon matrix. The main photodissociation channel via the SSC conformer produces formaldehyde–water complexes. The proposed photodissociation mechanism emphasizes that the conformers’ relative abundancies can significantly affect the photodissociation rate of the molecule. For example, in the case of high relative GAC and AAT concentrations, the ultraviolet photodissociation of glycolic acid requires the proceeding photo-isomerization of GAC and AAT to SSC.

Kinetics, product distribution and atmospheric implications of the gas-phase oxidation of allyl sulfides by OH radicals

Relative rate coefficients of the OH radical -initiated oxidation of allyl methyl sulfide (AMS, H2CCHCH2SCH3) and allyl ethyl sulfide (AES, H2CCHCH2SCH2CH3) have been measured at atmospheric pressure of synthetic air and 298 K: kAMS= (4.98 ± 1.42) and kAES= (6.88 ± 1.49) × 10−11 cm3 molecule−1 s−1 by means of in situ FTIR spectroscopy. In addition, the molar yields of the main reaction products of AMS with OH radicals formed in the absence and presence of nitric oxides (NOX) were determined to be the following: sulfur dioxide (95 ± 12) % and (51 ± 12) % for acrolein (50 ± 9) % and (41 ± 9) %. In the reaction of AES with OH radicals, the following molar yields were obtained: for sulfur dioxide (88 ± 13) % and (56 ± 12) % for acrolein (36 ± 9) % and (41 ± 9) %. The present results suggest that the abstraction at C3 plays an important role in the oxidation mechanism as the addition to the double bond. This work represents the first study of the OH radical interaction with AMS and AES carried out under atmospheric conditions. The atmospheric implications were discussed in terms of the atmospheric residence times of the sulfur-containing compounds studied and the products formed in the presence and absence of NOx. SO2 formation seems to be the main fate of the gas-phase allyl sulfides oxidation with significant acidifying potentials and short-chain aldehydes production like formaldehyde and acetaldehyde.

Rate coefficients for reactions of OH with aromatic and aliphatic volatile organic compounds determined by the multivariate relative rate technique

Abstract. The multivariate relative rate method was applied to a range of volatile organic compound (VOC) reactions with OH. This previously published method (Shaw et al., 2018) was improved to increase the sensitivity towards more slowly reacting VOCs, broadening the range of compounds which can be examined. A total of 35 room temperature relative rate coefficients were determined, eight of which have not previously been reported. Five of the new reaction rate coefficients were for large alkyl substituted mono-aromatic species recently identified in urban air masses, likely with large ozone production potentials. The new results (with kOH (296 K) values in units of 10−12 cm3 molec.−1 s−1) were n-butylbenzene, 11 (±4); n-pentylbenzene, 7 (±2); 1,2-diethylbenzene, 14 (±4); 1,3-diethylbenzene, 22 (±4); and 1,4-diethylbenzene, 16 (±4). Interestingly, whilst results for smaller VOCs agreed well with available structure–activity relationship (SAR) calculations, the larger alkyl benzenes were found to be less reactive than the SAR prediction, indicating that our understanding of the oxidation chemistry of these compounds is still limited. kOH (296 K) rate coefficients (in units of 10−12 cm3 molec.−1 s−1) for reactions of three large alkanes with OH were also determined for the first time: 2-methylheptane, 9.1 (±0.3); 2-methylnonane, 11.0 (±0.3); and ethylcyclohexane, 14.4 (±0.3), all in reasonable agreement with SAR predictions. Rate coefficients for the 27 previously studied OH + VOC reactions agreed well with available literature values, lending confidence to the application of this method for the rapid and efficient simultaneous study of gas-phase reaction kinetics.

Kinetics, mechanism and CH3C(O)CH3 formation in the Cl-initiated oxidation of 1,8-cineole at 298 K and atmospheric pressure

Kinetics of the reaction of chlorine atoms with the biogenic monoterpene 1,8-cineole was studied by gas chromatographywith flame ionization detection at 298 K and 760 Torr. The relative rate coefficient corrected by photolysis was determined to be (in cm3 molecule−1 s−1): (2.2 ± 0.2) × 10−10. Additionally, a product study was performed by solid-phase microextraction (SPME) coupled to gas chromatography-mass spectrometry (GC-MS). The following ketones were observed as products: acetone, 1,3,3-trimethyl-2-oxabiciclo[2.2.2]octan-5-one and 1,3,3-trimethyl-2-oxabicyclo[2.2.2]octan-6-one. Reactivity trends and a general mechanism of the title reaction, including acetone formation, are discussed to assess possible atmospheric implications.

Gas-phase degradation of 2-butanethiol initiated by OH radicals and Cl atoms: kinetics, product yields and mechanism at 298 K and atmospheric pressure.

Relative rate coefficients and product distribution of the reaction of 2-butanethiol (2butSH) with OH radicals and Cl atoms were obtained at atmospheric pressure and 298 K. The experiments were performed in a 480 L borosilicate glass photoreactor in synthetic air coupled to a long path “in situ” FTIR spectrometer. The rate coefficients obtained by averaging the values from different experiments were: kOH = (2.58 ± 0.21) × 10−11 cm3 per molecule per s and kCl = (2.49 ± 0.19) × 10−10 cm3 per molecule per s. The kinetic values were compared with related alkyl thiols and homologous alkyl alcohols, where it was found that thiols react faster with both oxidants, OH radicals and Cl atoms. SO2 and 2-butanone were the major products identified for the reactions of 2-butanethiol with OH radicals and Cl atoms. The product yield of the reaction of 2-butanethiol and OH radicals were (81 ± 2)%, and (42 ± 1)% for SO2 and 2-butanone, respectively. For the reactions of 2-butanethiol with Cl atom, yields of SO2 and 2-butanone were (59 ± 2)% and (39 ± 2)%, respectively. A degradation mechanism was proposed for the pathways that leads to formation of identified products. The product distribution observed indicated that the H-atom of the S–H group abstraction channel is the main pathway for the reaction of OH radicals and Cl atoms with 2-butanethiol.

H3O+, NO+ and O2+[rad] reactions with saturated and unsaturated monoketones and diones; focus on hydration of product ions

A selected ion flow tube, SIFT, study has been carried out for the reactions of the SIFT-MS reagent ions H3O+, NO+ and O2+ with 21 ketones, M, comprising 13 saturated monoketones of which 10 are linear and 3 are branched, 5 unsaturated monoketones and 3 diones. The collisional rate coefficients, kc, were calculated for the H3O+ reactions that all proceed via rapid proton transfer and the relative rate coefficients for the NO+ and O2+ reactions were obtained experimentally. The product ion distributions for all 63 reactions were obtained at two sample gas absolute humidity (0.5% and 5.5%), the higher humidity intended to simulate that of exhaled breath. A major objective was to understand how the product ions of the reactions formed hydrates, which is important for accurate quantification of metabolites in humid air samples by SIFT-MS and by secondary electrospray ionisation, SESI. The MH+ product ions of the H3O+ reactions readily hydrate at the higher humidity, the monohydrate being dominant for both the saturated and unsaturated ketones, whereas the dihydrate was dominant for the dione reactions. In the NO+ reactions, formation of the NO+M adduct ions was dominant for the saturated and unsaturated ketones, but charge transfer producing the M+ parent cation was very dominant in the dione reactions. The O2+ reactions all proceeded via dissociative charge transfer producing the parent cation M+ and closed shell and open shell cation fragments. Except for the dione parent cations, the M+ ions hydrated, as did the open shell fragment ions of the O2+ reactions, but the closed shell fragment ions did not hydrate.

Kinetics of the photolysis and OH reaction of 4-hydroxy-4-methyl-2-pentanone: Atmospheric implications

This study provides the first kinetic and mechanistic study of the photolysis of 4-hydroxy-4-methyl-2-pentanone (4H4M2P) and the determination of the temperature dependence of the relative rate coefficient for the reaction of OH radicals with 4H4M2P. The UV absorption spectrum of 4H4M2P was determined in the spectral range 200–360 nm. The photolysis frequency of this compound in the atmosphere was evaluated relative to actinometers and found to be J4H4M2Patm=4.2×10−3h−1, corresponding to a lifetime of about 10 days. Using 4H4M2P cross section measurements, an atmospheric effective quantum yield of 0.15 was calculated. The main primary photolysis products were acetone (121 ± 4) % and formaldehyde (20 ± 1) %. A low methanol yield of (3.0 ± 0.3) % was also determined. These results enabled us to propose a mechanistic scheme for the photolysis. Rate coefficients for the reaction of 4H4M2P with OH radicals were determined over the temperature range 298–354 K and the following Arrhenius expression was obtained: kOH+4M4H2P = (1.12 ± 0.40) × 10−12exp(461.5 ± 60/T) cm3 molecule−1 s−1. The lifetimes of 4H4M2P due to reaction with OH radicals has been estimated to ∼2.5 days and indicates that the gas-phase reaction with the OH could be the main loss process for this compound.

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.

Direct and relative rate coefficients for the gas-phase reaction of OH radicals with 2-methyltetrahydrofuran at room temperature

2-Methyltetrahydrofuran (2-MTHF) is a renewable green solvent, a platform molecule for organic syntheses and a potential automotive fuel or fuel additive that can be produced efficiently from lignocellulosic biomass. Its reaction with OH radicals is important concerning both of its atmospheric fate and combustion. The kinetics of the overall reaction OH + 2-MTHF → products (1) was studied at room temperature (T = 298 ± 1 K) using both direct and relative kinetic methods. The low pressure fast discharge flow (DF) experiments coupled with resonance fluorescence detection of OH have provided the direct rate coefficient of k 1 (298 K, 2.64 mbar He) = (1.21 ± 0.14 (±2σ)) × 10−11 cm3 molecule−1 s−1. The relative-rate experiments with gas-chromatographic analysis were performed at higher pressure in synthetic air using the reaction OH + cyclohexane (c-C6H12) → products (2) as reference. The determined rate coefficient ratio k 1/k 2 = 3.80 ± 0.17 (±2σ) has been converted to k 1(298 K, 1030 mbar air) = (2.65 ± 0.55 (±2σ)) × 10−11 cm3 molecule−1 s−1. This k 1 value agrees reasonably well with the only other rate coefficient reported which was determined also at higher pressures. Comparison with the DF result indicates a possible pressure dependence of the reaction. Impact of 2-MTHF on the chemistry of the atmosphere has been briefly discussed.

Understanding the C3H2cyclic-to-linear ratio in L1544

Aims. We aim to understand the high cyclic-to-linear $\rm C_3H_2$ ratio ($32 \pm 4$) observed toward L1544 by Spezzano et al. (2016). Methods. We combine a gas-grain chemical model with a physical model for L1544 to simulate the column densities of cyclic and linear $\rm C_3H_2$ observed toward L1544. The most important reactions for the formation and destruction of both forms of $\rm C_3H_2$ are identified, and their relative rate coefficients are varied to find the best match to the observations. Results. We find that the ratio of the rate coefficients of $\rm C_3H_3^+ + e^- \longrightarrow C_3H_2 + H$ for cyclic and linear $\rm C_3H_2$ must be $\sim 20$ in order to reproduce the observations, depending on the branching ratios assumed for the $\rm C_3H_3^+ + e^- \longrightarrow C_3H + H_2$ reaction. In current astrochemical networks it is assumed that cyclic and linear $\rm C_3H_2$ are formed in a 1:1 ratio in the aforementioned reactions. Laboratory studies and/or theoretical calculations are needed to confirm the results of our chemical modeling based on observational constraints.

Upscaling study of the cyclic solvent injection process for post‐chops reservoirs through numerical simulation

AbstractThe cyclic solvent injection (CSI) process has been suggested as the most promising solvent‐based recovery method for post‐CHOPS reservoirs. Six CSI experiments were performed in three sandpacks with different scales and wormhole locations. Numerical simulations were conducted to history‐match the six CSI experiments. The effects of uncertain parameters such as relative permeability, capillary pressure, reaction rate (foamy oil model), and dispersion coefficient on the history‐matching were studied. The sensitivity analysis indicated that relative permeability and capillary pressure significantly affected the production performance of the CSI process in the numerical simulation. In particular, capillary pressure played the greatest role in upscaling in both axial and radial directions. Furthermore, capillary pressure effects were aggravated when the wormhole was located in the top of the experimental model. Thus, all CSI experimental production data were matched successfully by tuning the capillary pressure based on the same matched relative permeability curves.A heavy oil post‐CHOPS reservoir in western Canada was evaluated for the CSI process at field scale. Wormholes were considered by applying the multi‐lateral well model. Post‐CHOPS conditions were established by history‐matching the field's production of oil and water. The parameters obtained from the history match upscaling studies were adopted in simulating the subsequent CSI process and were set with certain constraints to consider its uncertainty at field scale. The recovery factor after ten years of the CSI process was in the range of 13.5–16.0 %.

Unimolecular Decomposition Rate of the Criegee Intermediate (CH3)2COO Measured Directly with UV Absorption Spectroscopy.

The unimolecular decomposition of (CH3)2COO and (CD3)2COO was measured by direct detection of the Criegee intermediate at temperatures from 283 to 323 K using time-resolved UV absorption spectroscopy. The unimolecular rate coefficient kd for (CH3)2COO shows a strong temperature dependence, increasing from 269 ± 82 s(-1) at 283 K to 916 ± 56 s(-1) at 323 K with an Arrhenius activation energy of ∼6 kcal mol(-1). The bimolecular rate coefficient for the reaction of (CH3)2COO with SO2, kSO2, was also determined in the temperature range 283 to 303 K. Our temperature-dependent values for kd and kSO2 are consistent with previously reported relative rate coefficients kd/kSO2 of (CH3)2COO formed from ozonolysis of tetramethyl ethylene. Quantum chemical calculations of kd for (CH3)2COO are consistent with the experiment, and the combination of experiment and theory for (CD3)2COO indicates that tunneling plays a significant role in (CH3)2COO unimolecular decomposition. The fast rates of unimolecular decomposition for (CH3)2COO measured here, in light of the relatively slow rate for the reaction of (CH3)2COO with water previously reported, suggest that thermal decomposition may compete with the reactions with water and with SO2 for atmospheric removal of the dimethyl-substituted Criegee intermediate.

Reactivity of stabilized Criegee intermediates (sCIs) from isoprene and monoterpene ozonolysis toward SO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; and organic acids

Abstract. Oxidation processes in Earth's atmosphere are tightly connected to many environmental and human health issues and are essential drivers for biogeochemistry. Until the recent discovery of the atmospheric relevance of the reaction of stabilized Criegee intermediates (sCIs) with SO2, atmospheric oxidation processes were thought to be dominated by a few main oxidants: ozone, hydroxyl radicals (OH), nitrate radicals and, e.g. over oceans, halogen atoms such as chlorine. Here, we report results from laboratory experiments at 293 K and atmospheric pressure focusing on sCI formation from the ozonolysis of isoprene and the most abundant monoterpenes (α-pinene and limonene), and subsequent reactions of the resulting sCIs with SO2 producing sulfuric acid (H2SO4). The measured total sCI yields were (0.15 ± 0.07), (0.27 ± 0.12) and (0.58 ± 0.26) for α-pinene, limonene and isoprene, respectively. The ratio between the rate coefficient for the sCI loss (including thermal decomposition and the reaction with water vapour) and the rate coefficient for the reaction of sCI with SO2, k(loss) /k(sCI + SO2), was determined at relative humidities of 10 and 50%. Observed values represent the average reactivity of all sCIs produced from the individual alkene used in the ozonolysis. For the monoterpene-derived sCIs, the relative rate coefficients k(loss) / k(sCI + SO2) were in the range (2.0–2.4) × 1012 molecules cm−3 and nearly independent of the relative humidity. This fact points to a minor importance of the sCI + H2O reaction in the case of the sCI arising from α-pinene and limonene. For the isoprene sCIs, however, the ratio k(loss) / k(sCI + SO2) was strongly dependent on the relative humidity. To explore whether sCIs could have a more general role in atmospheric oxidation, we investigated as an example the reactivity of acetone oxide (sCI from the ozonolysis of 2,3-dimethyl-2-butene) toward small organic acids, i.e. formic and acetic acid. Acetone oxide was found to react faster with the organic acids than with SO2; k(sCI + acid) / k(sCI + SO2) = (2.8 ± 0.3) for formic acid, and k(sCI + acid) / k(sCI + SO2) = (3.4 ± 0.2) for acetic acid. This finding indicates that sCIs can play a role in the formation and loss of other atmospheric constituents besides SO2.