Gas-phase Reaction Rate Research Articles

Gas-Phase Reaction Kinetic Study of a Series of Methyl-Butenols with Ozone under Atmospherically Relevant Conditions.

Methyl-butenols are a category of oxygenated biogenic volatile organic compounds emitted by plants as part of their natural metabolic processes. This study examines the gas-phase reactions of ozone (O3) with five methyl-butenols (2-methyl-3-buten-2-ol, 3-methyl-2-buten-1-ol, 3-methyl-3-buten-1-ol, 2-methyl-3-buten-1-ol, and 3-methyl-3-buten-2-ol) under atmospheric conditions at a temperature of (298 ± 2) K and pressure of (1000 ± 10) mbar. The experimental values for the gas-phase reaction rate coefficients obtained in this study, by using the relative rate method, are as follows (in cm3 molecule-1 s-1): k(3-methyl-2-buten-1-ol + O3) = (311 ± 20) × 10-18, k(2-methyl-3-buten-2-ol + O3) = (9.55 ± 1.04) × 10-18, k(3-methyl-3-buten-1-ol + O3) = (7.29 ± 0.46) × 10-18, k(2-methyl-3-buten-1-ol + O3) = (4.25 ± 0.29) × 10-18, and k(3-methyl-3-buten-2-ol + O3) = (62.9 ± 6.8) × 10-18. The results are discussed in detail, with particular emphasis on the degree and type of substitutions of the double bond. The determined rate coefficient values are also compared to the available literature data and with estimates of the structure-activity relationship. Additionally, the atmospheric implications toward the tropospheric lifetime and photochemical ozone generation potential for the investigated compounds are provided, which highlight the atmospheric impact of methyl-butenol decomposition into the lower atmosphere.

Gas-Phase Kinetics of a Series of cis-3-Hexenyl Esters with OH Radicals under Simulated Atmospheric Conditions.

The present relative kinetic study reports on the experimentally determined gas-phase reaction rate coefficients of OH radicals with a series of seven cis-3-hexenyl esters. The experiments were carried out in the environmental simulation chamber made of quartz from the "Alexandru Ioan Cuza" University of Iasi (ESC-Q-UAIC), Romania, at a temperature of (298 ± 2) K and a total air pressure of (1000 ± 10) mbar. In situ long-path Fourier transform infrared (FTIR) spectroscopy was used to monitor cis-3-hexenyl formate (Z3HF, (Z)-CH3CH2CH═CH(CH2)2OC(O)H), cis-3-hexenyl acetate (Z3HAc, (Z)-CH3CH2CH═CH(CH2)2OC(O)CH3), cis-3-hexenyl isobutyrate (Z3HiB, (Z)-CH3CH2CH═CH(CH2)2OC(O)CH(CH3)2), cis-3-hexenyl 3-methylbutanoate (Z3H3MeB, (Z)-CH3CH2CH═CH(CH2)2OC(O)CH2CH(CH3)2), cis-3-hexenyl hexanoate (Z3HH, (Z)-CH3CH2CH═CH(CH2)2OC(O)(CH2)4CH3), cis-3-hexenyl cis-3-hexenoate (Z3HZ3H, (Z,Z)-CH3CH2CH═CH(CH2)2OC(O)CH2CH═CHCH2CH3), cis-3-hexenyl benzoate (Z3HBz, (Z)-CH3CH2CH═CH(CH2)2OC(O)C6H5), and the reference compounds. The following reaction rate coefficients (in 10-11 cm3 molecule-1 s-1) were obtained for the OH radical-initiated gas-phase oxidation of cis-3-hexenyl esters: (4.13 ± 0.45) for Z3HF, (4.19 ± 0.38) for Z3HAc, (4.84 ± 0.39) for Z3HiB, (5.39 ± 0.61) for Z3H3MeB, (7.00 ± 0.56) for Z3HH, (10.58 ± 1.40) for Z3HZ3H, and (3.41 ± 0.28) for Z3HBz. The results are discussed in terms of hexenyl ester reactivity and compared with the available literature data and structure-activity relationship (SAR) estimates. The atmospheric implications based on the average lifetimes of the investigated cis-3-hexenyl esters are discussed in the present study. The gas-phase rate coefficients for OH radical reactions are given herein for the first time for cis-3-hexenyl isobutyrate, cis-3-hexenyl 3-methylbutanoate, cis-3-hexenyl hexanoate cis-3-hexenyl cis-3-hexenoate, and cis-3-hexenyl benzoate. The newly determined gas-phase reaction rate coefficients provide new information for existing kinetic databases and contribute to the further development of SAR methodologies useful for predicting the reactivity of oxygenated volatile organic compounds.

Production of combustible gas via incorporating CO2 to pyrolysis of medicinal herbal waste

With the recent increase in the utilization of medicinal herbs, the generation of medicinal herbal waste has increased. However, conventional protocols for solid waste management (landfill and incineration) present environmental threats considering the complex chemical composition of medicinal herbal waste. Thus, this study introduces a thermochemical approach for managing medicinal herbal waste, focusing on conversion of red ginseng marc (RGM) into energy resource. This study explores an innovative strategy to maximize the production of pyrogenic gases using CO2 form improved syngas generation. The experimental results revealed an enhancement in CO from the pyrolysis of RGM under the CO2 condition in reference with the N2 condition, which was ascribed to gas-phased homogeneous reaction of CO2 with volatile matters liberated from RGM. Moreover, gas-phase reactions have proven to be effective in decreasing the benzene analogs, especially polycyclic aromatic hydrocarbons (PAHs), in pyrogenic liquids. To accelerate the gas-phase reaction rate, a nickel (Ni)-based catalyst was employed for the RGM pyrolysis. The introduction of Ni catalyst to the gas-phase reaction led to an CO enhancement (272 %) from the RGM pyrolysis in the presence of CO2. All experimental observations highlight the potential of incorporating CO2 in thermochemical conversion of RGM as an innovative way to enhance energy recovery.

Particle-resolved numerical simulations of char particle combustion in isotropic turbulence

In the present study, two-dimensional particle-resolved numerical simulations of char particle combustion are performed. A series of cases are considered, with varying turbulence intensities and heterogeneous reaction rates. The impact of turbulence and Stefan flow on char particle combustion is examined. It is shown that the cases with higher turbulence intensity and heterogeneous reaction rate exhibit higher mean gas-phase temperatures and reaction rates. The range of the Stefan flow Reynolds number (ReS) increases as the value of heterogeneous reaction rate increases. Additionally, higher turbulence intensity is associated with an increased range of ReS. The drag force coefficient of burning particles is analyzed. The results show that turbulence induces fluctuations of drag force coefficient, and increasing the turbulent velocity broadens the drag force coefficient fluctuation amplitude. The particle drag force is increased with increasing heterogeneous reaction rate. The pressure and viscous components of the drag force are examined. It is revealed that the increase of heterogeneous reaction rate alters the pressure distribution on the particle surface, resulting in the increase of pressure drag force, while the viscous drag force remains almost unchanged.

Revisiting the Gas-phase Chemical Rate Coefficients at High Temperatures in CLOUDY

A two-body gas-phase reaction rate coefficient can be given by the usual Arrhenius-type formula which depends on temperature. The UMIST Database for Astrochemistry is a widely used database for reaction rate coefficients. They provide fittings for coefficients valid over a particular range of temperatures. The permissible upper-temperature limits vary over a wide range: from 100 to 41,000 K. A wide range of temperatures occurs in nature; thus, it requires evaluating the rate coefficients at temperatures outside the range of validity. As a result, a simple extrapolation of the rate coefficients can lead to unphysically large values at high temperatures. These result in unrealistic predictions. Here we present a solution to prevent the gas-phase reaction coefficients from diverging at a very high temperature. We implement this into the spectral synthesis code CLOUDY which operates over a wide range of temperatures from CMB to 1010 K subject to different astrophysical environments.

Theoretical and experimental study of the OH radical with 3‐bromopropene gas phase reaction rate coefficients temperature dependence

AbstractIn this work, the rate‐determining steps of the OH radical + 3‐bromopropene gas phase reaction were studied, which could explain for the possible negative activation energy observed in experiments. To obtain new kinetic parameters and data for critical revisions, a reinvestigation of the rate coefficient (k) and its temperature dependence was carried out using the PLP‐LIF technique, in the 254‐ to 371‐K range. Moreover, quantum‐mechanical and canonical variational transition state theory calculations were performed, taking into consideration four OH addition and two β‐hydrogen atom abstraction reaction channels. The proposed kinetic model fits to the observed experimental Arrhenius behavior, and three not negligible reaction pathways are described for the first time.

Updating and evaluating the NH3 gas-phase chemical mechanism of MOZART-4 in the WRF-Chem model

The accuracy of determining atmospheric chemical mechanisms is a key factor in air pollution prediction, pollution-cause analysis and the development of control schemes based on air quality model simulations. However, the reaction of NH3 and OH to generate NH2 and its subsequent reactions are often ignored in the MOZART-4 chemical mechanism. To solve this problem, the gas-phase chemical mechanism of NH3 was updated in this study. Response surface methodology (RSM), integrated gas-phase reaction rate (IRR) diagnosis and process analysis (PA) were used to quantify the influence of the updated NH3 chemical mechanism on the O3 simulated concentration, the nonlinear response relationship of O3 and its precursors, the chemical reaction rate of O3 generation and the meteorological transport process. The results show that the updated NH3 chemical mechanism can reduce the error between the simulated and observed O3 concentrations and better simulate the O3 concentration. Compared with the Base scenario (original chemical mechanism simulated), the first-order term of NH3 in the Updated scenario (updated NH3 chemical mechanism simulated) in RSM passed the significance test (p < 0.05), indicating that NH3 emissions have an influence on the O3 simulation, and the effects of the updated NH3 chemical mechanism on NOx-VOC-O3 in different cities are different. In addition, the analysis of chemical reaction rate changes showed that NH3 can affect the generation of O3 by affecting the NOx concentration and NOx circulation with radicals of OH and HO2 in the Updated scenario, and the change of pollutant concentration in the atmosphere leads to the change of meteorological transmission, eventually leading to the reduction of O3 concentration in Beijing. In conclusion, this study highlights the importance of atmospheric chemistry for air quality models to model atmospheric pollutants and should attract more research focus.

Numerical simulation and validation of reaction mechanism for the Siemens process in silicon production

The Siemens process is the most widely used silicon production routine for photovoltaic applications. However, the complicated chemistry in deposition reactor has not yet been fully understood, although there has been much research on it. In this paper, a modified reaction kinetic model was proposed to represent the gas phase and surface reactions based on the literature. The thermodynamic properties of gas phase components were re-evaluated by density functional theory since the reverse reaction rate of gas phase reaction is highly dependent on Gibbs energy change (ΔG). Most of our efforts were devoted to validating the reaction mechanism. The modified reaction model was analyzed and compared with published experimental data in two different reaction paths, deposition from trichlorosilane and etch from hydrochloride, respectively. The epitaxial growth rate could be predicted by the modified reaction model under a wide range of operating conditions.The results could provide a theoretical basis for possible computational fluid dynamics (CFD) simulations of industrial Siemens reactor in the future.

Reliable Gas Phase Reaction Rates at Affordable Cost by Means of the Parameter-Free JunChS-F12 Model Chemistry.

A recently developed strategy for the computation at affordable cost of reliable barrier heights ruling reactions in the gas phase (junChS, [Barone, V.; J. Chem. Theory Comput. 2021, 17, 4913-4928]) has been extended to the employment of explicitly correlated (F12) methods. A thorough benchmark based on a wide range of prototypical reactions shows that the new model (referred to as junChS-F12), which employs cost-effective revDSD-PBEP86-D3(BJ) reference geometries, has an improved performance with respect to its conventional counterpart and outperforms the most well-known model chemistries without the need of any empirical parameter and at an affordable computational cost. Several benchmarks show that revDSD-PBEP86-D3(BJ) structures and force fields provide zero point energies and thermal contributions, which can be confidently used, together with junChS-F12 electronic energies, for obtaining accurate reaction rates in the framework of the master equation approach based on the ab initio transition-state theory.

Low-Temperature Gas-Phase Kinetics of Ethanol-Methanol Heterodimer Formation.

The structures of gas-phase noncovalently bound clusters have long been studied in supersonic expansions. This method of study, while providing a wealth of information about the nature of noncovalent bonds, precludes observation of the formation of the cluster, as the clusters form just after the orifice of the pulsed valve. Here, we directly observe formation of ethanol-methanol dimers via microwave spectroscopy in a controlled cryogenic environment. Time profiles of the concentration of reagents in the cell yielded gas-phase reaction rate constants of kMe-g = (2.8 ± 1.4) × 10-13 cm3 molecule-1 s-1 and kMe-t = (1.6 ± 0.8) × 10-13 cm3 molecule-1 s-1 for the pseudo-second-order ethanol-methanol dimerization reaction at 8 K. The relaxation cross section between the gauche and trans conformers of ethanol was also measured using the same technique. In addition, thermodynamic relaxation between conformers of ethanol over time allowed for selection of conformer stoichiometry in the ethanol-methanol dimerization reaction, but no change in the ratio of dimer conformers was observed with changing ethanol monomer stoichiometry.

Effects of chemical boundary conditions on simulated O3 concentrations in China and their chemical mechanisms

Chemical boundary conditions (BCs) are important inputs for regional chemical transport models. In this study, we use the brute-force method (BFM), process analysis (PA) and response surface model (RSM) to quantify the effects of BCs on simulated O3 concentrations in different regions of China by the weather research and forecasting with chemistry (WRF–Chem) model. We combine the model with an integrated gas-phase reaction rate (IRR) tool to further analyze the changes in the O3 chemical mechanisms. Our results show that the simulated O3 concentrations in western cities are significantly affected by the O3 in the BCs (BC-O3), which can increase the maximum simulated O3 concentration, such as in Lanzhou (36.6 μg/m3, 26.3 %), Wuhai (30.1 μg/m3, 25.5 %) and Urumqi (50.7 μg/m3, 41.2 %). In contrast, O3 generation in the eastern region is dominated by emissions. Subsequently, we compare the reaction rate changes in O3 generation and consumption under the effects of BC-O3 in the western city of Urumqi and the eastern city of Beijing. The results show that in Beijing, the O3 concentration and the related chemical reaction rates undergo little change, while in Urumqi, the concentration and reaction rates have significant differences. The BC-O3 significantly accelerates the O3 photochemical reaction process in Urumqi, resulting in increased O3 generation and consumption reaction rates; additionally, there may be a chemical reaction pathway for the formation of O3: BC-O3 + NO → NO2 + hv → O + O2 → O3. BC-O3 transmission is the main pathway of changes in the simulated O3 concentration in the study area, and the chemical reactions between BC-O3 and local pollutants are primarily characterized by O3 consumption. In conclusion, the study shows the importance of BCs for regional model simulation while providing supporting information for O3 formation in model studies.

Investigations into the gas-phase photolysis and OH radical kinetics of nitrocatechols: implications of intramolecular interactions on their atmospheric behaviour

Abstract. The Environmental Simulation Chamber made of Quartz from the University “Alexandru Ioan Cuza” (ESC-Q-UAIC), at Iasi, Romania, was used to investigate the gas-phase reaction rate coefficients for four nitrocatechols toward OH radicals under simulated atmospheric conditions. Employing relative rate techniques at a temperature of 298 ± 2 K and a total air pressure of 1 atm, the obtained rate coefficients (in 10−12 cm3 s−1) were as follows: k3NCAT = (3.41 ± 0.37) for 3-nitrocatechol and k5M3NCAT = (5.55 ± 0.45) for 5-methyl-3-nitrocatechol at 365 nm, using CH3ONO photolysis as OH radicals source and dimethyl ether and cyclohexane as reference compounds, and k4NCAT = (1.27 ± 0.19) for 4-nitrocatechol and k4M5NCAT = (0.92 ± 0.14) for 4-methyl-5-nitrocatechol at 254 nm using H2O2 as OH radicals source and dimethyl ether and methanol as reference compounds. The photolysis rates in the actinic region, scaled to atmospheric relevant conditions by NO2 photolysis, were evaluated for 3-nitrocatechol and 5-methyl-3-nitrocatechol: J3NCAT = (3.06 ± 0.16) × 10−4 s−1 and J5M3NCAT = (2.14 ± 0.18) × 10−4 s−1, respectively. The photolysis rate constants at 254 nm were measured for 4-nitrocatechol and 4-methyl-5-nitrocatechol and the obtained values are J4NCAT = (6.7 ± 0.1) × 10−5 s−1 and J4M5NCAT = (3.2 ± 0.3) × 10−5 s−1. Considering the obtained results, our study suggests that photolysis may be the main degradation process for 3-nitrocatechol and 5-methyl-3-nitrocatechol in the atmosphere, with a photolytic lifetime in the atmosphere of up to 2 h. Results are discussed in terms of the reactivity of the four nitrocatechols under investigation toward OH-radical-initiated oxidation and their structural features. The rate coefficient values of the nitrocatechols are also compared with those estimated from the structure-activity relationship for monocyclic aromatic hydrocarbons and assessed in relation to their gas-phase IR spectra. Additional comparison with similar compounds is also presented, underlining the implications toward possible degradation pathways and atmospheric behaviour.

Features of exhaust gases afterburning in a converter when using two-tier oxygen lances for refining

The theoretical substantiation was carried out for increasing the efficiency of converter gases afterburning in the unit with a two­tier supply of multi­pulse oxygen jets and combustion of CO to CO2 in the channel flow of gases leaving the reaction zone. The authors made the thermodynamic analysis of the process of exhaust gases afterburning in converter cavity when using two­tier oxygen lances for refining. It is shown that when oxygen gas jets are blown through the upper­tier nozzles with a flow rate of 10 – 40 % of the total minute flow rate, a sufficiently complete afterburning of carbon monoxide CO is not provided. The limiting factors are the uneven amount and disorganized output of the CO formed in the reaction zones during various operation periods, low efficiency of mixing the waste stream with high­speed gas jets and an excessively excessive amount of oxygen supplied for afterburning, insufficient mixing of the components of the gas phase and low reaction rate. It is shown that when the conditions are provided for CO afterburning to the concentration ratio in the gas phase, temperature of the exhaust gas in the converter cavity can increase from 1800 to 2000 K, then the thermal effect of the exothermic reaction decreases. The amount of oxygen injected for CO afterburning must correspond to the residual carbon content in the metal at m3/min ≈ 100 [Сост ] %. Excess of oxygen in the gas phase and presence of a significant amount of neutral gas significantly reduce the utilization rate of the generated heat in the unit.

The fate of methyl salicylate in the environment and its role as signal in multitrophic interactions

Phytohormones emitted into the atmosphere perform many functions relating to the defence, pollination and competitiveness of plants. To be effective, their atmospheric lifetimes must be sufficient that these signals can be delivered to their numerous recipients.We investigate the atmospheric loss processes for methyl salicylate (MeSA), a widely emitted plant volatile. Simulation chambers were used to determine gas-phase reaction rates with OH, NO3, Cl and O3; photolysis rates; and deposition rates of gas-phase MeSA onto organic aerosols. Room temperature rate coefficients are determined (in units of cm3 molecule−1 s−1) to be (3.20 ± 0.46) × 10−12, (4.19 ± 0.92) × 10−15, (1.65 ± 0.44) × 10−12 and (3.33 ± 2.01) × 10−19 for the reactions with OH, NO3, Cl and O3 respectively. Photolysis is negligible in the actinic range, despite having a large reported near-UV chromophore. Conversely, aerosol uptake can be competitive with oxidation under humid conditions, suggesting that this compound has a high affinity for hydrated surfaces. A total lifetime of gas-phase MeSA of 1–4 days was estimated based on all these loss processes.The competing sinks of MeSA demonstrate the need to assess lifetimes of semiochemicals holistically, and we gain understanding of how atmospheric sinks influence natural communication channels within complex multitrophic interactions. This approach can be extended to other compounds that play vital roles in ecosystems, such as insect pheromones, which may be similarly affected during atmospheric transport.

Gas-Phase Reactions of Deprotonated Nucleobases with H, N, and O Atoms.

Complex organic molecules, the hallmark of terrestrial life, are increasingly detected in exotic environments throughout the universe. Our studies probe the ion chemistry of these biomolecules. We report gas-phase reaction rate constants for five deprotonated nucleobases (adenine, cytosine, guanine, thymine, and uracil) reacting with the atomic species H, N, and O. Hydrogen atoms react at moderate rates via associative electron detachment. Oxygen atom reactions occur more rapidly, generating complex product distributions; reaction pathways include associative electron detachment, substitution of the hydrogen atom by an oxygen atom, and generation of OCN-. Nitrogen atoms do not react with the nucleobase anions. The reaction thermodynamics were investigated computationally, and reported product channels are exothermic. Many of the proposed products have been observed in various astrochemical environments. These reactions provide insight into chemical processes that may occur at the boundaries between diffuse and dense interstellar clouds and in complex extraterrestrial ionospheres.

Cluster-π Interactions Cause Size-Selective Reactivity of Cationic Silver Clusters with Acetylene: The Distinctive Ag7+[C2H2

Utilizing a customized multiple-ion laminar flow tube reactor in tandem with a triple quadrupole mass spectrometer, we report a study of the gas-phase reactivity of Agn+ clusters with acetylene. Well-resolved Agn+ clusters (n = 1-20) are produced by a self-designed magnetron sputtering source (MagS); however, on their reactions with acetylene under sufficient collisional conditions, only Ag7+[C2H2] is produced with a reasonable intensity. DFT calculations reveal that Agn+ clusters do not form strong Ag-C bonds with C2H2 and Ag7+[C2H2] bears larger binding energy than the other Agn+[C2H2] although within similar cluster-π interactions. Besides gas-phase reaction rate estimation, the relatively large noncovalent cluster-π interaction in Ag7+[C2H2] is fully demonstrated via topological analysis and natural bonding orbital analysis. Also, we illustrate both thermodynamically and kinetically favored channels in producing the Ag7+[C2H2]. This study helps in understanding metal-involved noncovalent bonds and how such weak interactions are able to tune the material function and biological activity.

Flame Growth Around a Spherical Solid Fuel in Low Speed Forced Flow in Microgravity

To further our understanding of flammability and quenching limit of thick solid fuels, a microgravity experiment Growth and Extinction Limits is to be conducted aboard the International Space Station with the emphasis to quantify the effect of the flame heat loss to the thermally thick solid interior by directly measuring the sub-surface temperature gradient. A precursor microgravity combustion experiment in the Burning and Suppression of Solids (BASS) project was used to assess the experimental operation and validate the accompanied numerical model. The present paper reports the development of the flame model over a solid sphere in low-speed pure convective flow (less than 100 cm/s). Computed time sequence result of one of the BASS conditions is presented. The combination of gas phase reaction rate, solid internal temperature and surface heat flux distribution reveals the effect of solid in-depth heat-up on flame growth. The experimental observations agree with the trend predicted by the model. For thick solids, flame quenching limit in low speed flow is not only a function of flow speed but also the degree of solid interior heat-up. Flammability limit can have profound implication to the current spacecraft fire protection protocol that requires turning-off of circulation flow in case of detected fire. The present and the follow-up studies will provide more quantitative estimate of the low velocity-quenching limit with heated samples. For the Polymethylmethacrylate spheres investigated, the limit is lower than 2 cm/s in air.

Low temperature gas phase reaction rate coefficient measurements: Toward modeling of stellar winds and the interstellar medium

AbstractStellar winds of Asymptotic Giant Branch (AGB) stars are responsible for the production of ∼85% of the gas molecules in the interstellar medium (ISM), and yet very few of the gas phase rate coefficients under the relevant conditions (10 – 3000 K) needed to model the rate of production and loss of these molecules in stellar winds have been experimentally measured. If measured at all, the value of the rate coefficient has often only been obtained at room temperature, with extrapolation to lower and higher temperatures using the Arrhenius equation. However, non-Arrhenius behavior has been observed often in the few measured rate coefficients at low temperatures. In previous reactions studied, theoretical simulations of the formation of long-lived pre-reaction complexes and quantum mechanical tunneling through the barrier to reaction have been utilized to fit these non-Arrhenius behaviours of rate coefficients.Reaction rate coefficients that were predicted to produce the largest change in the production/loss of Complex Organic Molecules (COMs) in stellar winds at low temperatures were selected from a sensitivity analysis. Here we present measurements of rate coefficients using a pulsed Laval nozzle apparatus with the Pump Laser Photolysis - Laser Induced Fluorescence (PLP-LIF) technique. Gas flow temperatures between 30 – 134 K have been produced by the University of Leeds apparatus through the controlled expansion of N2 or Ar gas through Laval nozzles of a range of Mach numbers between 2.49 and 4.25.Reactions of interest include those of OH, CN, and CH with volatile organic species, in particular formaldehyde, a molecule which has been detected in the ISM. Kinetics measurements of these reactions at low temperatures will be presented using the decay of the radical reagent. Since formaldehyde and the formal radical (HCO) are potential building blocks of COMs in the interstellar medium, low temperature reaction rate coefficients for their production and loss can help to predict the formation pathways of COMs observed in the interstellar medium.

A simplified model on carbon monoxide yield in burning of polymeric solids containing flame retardants

Recent advances in Microscale Combustion Calorimetry (MCC) allow polymeric solids to be pyrolyzed and oxidized separately at the milligram scale, and the combustion gases, O2, CO, and CO2 to be measured using in-line gas analyzers. A simplified two-step reaction mechanism, which involves a CO generation step and a CO oxidation step, was developed to better describe the chemical reaction scheme that generates/oxidizes these products within the premixed combustor. Different incomplete combustion conditions were attained by varying the MCC combustor temperature and a numerical model of the combustor was developed to simulate the species evolution. Kinetics parameters were found by minimizing the errors in fitting the simulated results with the experiments. The two-step method was employed to examine halogen- and phosphorous-containing polymers of known compositions. The halogen additives were found to decrease gas phase reaction rate, whereas the phosphorous additives do not show significant effect. In cone calorimeter fire tests, both additives inhibit combustion efficiency by promoting soot formation.

Prediction of Chain Propagation Rate Constants of Polymerization Reactions in Aqueous NIPAM/BIS and VCL/BIS Systems.

Microgels have a wide range of possible applications and are therefore studied with increasing interest. Nonetheless, the microgel synthesis process and some of the resulting properties of the microgels, such as the cross-linker distribution within the microgels, are not yet fully understood. An in-depth understanding of the synthesis process is crucial for designing tailored microgels with desired properties. In this work, rate constants and reaction enthalpies of chain propagation reactions in aqueous N-isopropylacrylamide/N,N'-methylenebisacrylamide and aqueous N-vinylcaprolactam/N,N'-methylenebisacrylamide systems are calculated to identify the possible sources of an inhomogeneous cross-linker distribution in the resulting microgels. Gas-phase reaction rate constants are calculated from B2PLYPD3/aug-cc-pVTZ energies and B3LYPD3/tzvp geometries and frequencies. Then, solvation effects based on COSMO-RS are incorporated into the rate constants to obtain the desired liquid-phase reaction rate constants. The rate constants agree with experiments within a factor of 2-10, and the reaction enthalpies deviate less than 5 kJ/mol. Further, the effect of rate constants on the microgel growth process is analyzed, and it is shown that differences in the magnitude of the reaction rate constants are a source of an inhomogeneous cross-linker distribution within the resulting microgel.