Basis Of Kinetic Data Research Articles

Relative influence of helium and nitrogen carrier gases on analyte ion branching ratios in SIFT-MS

Nitrogen carrier gas is now being used more frequently for SIFT-MS analyses than helium for the reasons of cost and supply. Yet the extensive kinetics database required has largely been compiled using data obtained in helium carrier gas. This paper asks the question: can the helium-based kinetics library be used with confidence for analyses in nitrogen carrier gas? To investigate this, the rate coefficients and product ion distributions for the reactions of H3O+, NO+ and O2+● with three monoterpenes, β-pinene, camphene and (R)-(+)-limonene, and the specific reactions (a) H3O+ with 2-propanol, (b) O2+● with acetone, (c) NO+ with acetaldehyde and (d) NO+ with 2,3-butanedione have been explored in both helium and nitrogen carrier gases using a Profile 3 SIFT-MS instrument. These reactions were chosen because several primary reaction mechanisms are involved, including proton transfer (a), charge transfer (b), parallel hydride ion transfer and adduct ion formation (c) and parallel charge transfer and adduct ion formation (d). The detailed results show that for the diverse monoterpene reactions that have multiple product ions and for the pure bimolecular reactions (a) and (b), the reaction kinetics in both helium and nitrogen carrier gases are essentially identical. However, reactions (c) and (d) in which adduct ions are partially formed exhibit a slow carrier gas pressure dependence in helium, but a much greater carrier gas pressure dependence in nitrogen, and different product ion distributions. The conclusion is drawn that for pure bimolecular reactions, e.g. (a) and (b), the helium-obtained kinetics data can be used with confidence for trace gas analysis by SIFT-MS in nitrogen carrier gas, whereas kinetics data for ion-molecule reactions that involve adduct ion formation must be obtained by measurements under the specific pressure (and temperature) of the nitrogen carrier gas at which gas analyses are to be performed.

Graphene oxide/Mg-Zn-Al layered double hydroxide for efficient removal of doxycycline from water: Taguchi approach for optimization

Graphene oxide/Mg-Zn-Al layered double hydroxide (GMZA) was synthesized and applied for the adsorptive removal of doxycycline. The material was characterized by FTIR, Raman, XRD, XPS, SEM with EDX, TEM and TGA-DTA. The variables of the adsorption process (contact time, pH, adsorbent dose and initial concentration) were optimized by Taguchi method. The optimum levels of variables were: contact time = 90 min; pH = 8; adsorbent dose = 15 mg and initial concentration of doxycycline = 100 mg/L. The material showed enhanced adsorption capacity (429.33 mg/g) for doxycycline. The equilibrium adsorption data fitted well to Freundlich isotherm model with R2 > 0.99 and χ2 ≤ 0.40. The pseudo-second order kinetic model was the best fit model with R2 > 0.998 and χ2 ≤ 0.20. The thermodynamic parameters suggested the endothermic and spontaneous nature of adsorption process. The adsorption mechanism was explained on the basis of kinetic data, FTIR and Raman spectroscopy. The results suggested the involvement of electrostatic interaction, π-π interaction and H-bonding in the adsorption of doxycycline on the adsorbent. Adsorption/desorption test demonstrated that the material can be used upto 5 cycles.

Characterization and modeling of concurrent precipitation in Mg-Al-Sn alloys using an improved Kampmann-Wagner numerical (KWN) model

The concurrent precipitation microstructure of Mg17Al12 and Mg2Sn phases in AT72 (Mg-7Al-2Sn) magnesium alloy was quantitatively characterized using Scanning Transmission Electron Microscopy (STEM) based techniques. An improved Kampmann-Wagner numerical (KWN) model taking into account of the effects of non-spherical precipitates on growth kinetics and coupled with multicomponent thermodynamic and kinetic databases of magnesium alloys was used to simulate the evolution of the concurrent precipitation microstructure. Furthermore, the age hardening behavior of AT72 alloy was predicted by coupling the improved KWN model with a classical precipitation strengthening model. Simulation results show that a lower aging temperature will lead to finer and higher number density of both types of precipitates, providing improved aging hardening response. The addition of Al to Mg-Sn alloys can increase the driving force and precipitation kinetics of Mg2Sn phase. High-throughput KWN simulation was performed on the Mg-Al-Sn alloy system to demonstrate the application of the improved KWN model in optimizing the composition and heat treatment procedure in precipitation strengthened alloys.

Gas-Phase Reactivity of OH Radicals With Ammonia (NH3) and Methylamine (CH3NH2) at Around 22 K

Interstellar molecules containing N atoms, such as ammonia (NH3) and methylamine (CH3NH2), could be potential precursors of amino acids like the simplest one, glycine (NH2CH2COOH). The gas-phase reactivity of these N-bearing species with OH radicals, ubiquitous in the interstellar medium, is not known at temperatures of cold dark molecular clouds. In this work, we present the first kinetic study of these OH-reactions at around 22 K and different gas densities [(3.4–16.7) × 1016 cm−3] in helium. The obtained rate coefficients, with ± 2σ uncertainties, can be included in pure gas-phase or gas-grain astrochemical models to interpret the observed abundances of NH3and CH3NH2. We observed an increase ofk1andk2with respect to those previously measured by others at the lowest temperatures for which rate coefficients are presently available: 230 and 299 K, respectively. This increase is about 380 times for NH3and 20 times for CH3NH2. Although the OH + NH3reaction is included in astrochemical kinetic databases, the recommended temperature dependence fork1is based on kinetic studies at temperatures above 200 K. However, the OH + CH3NH2reaction is not included in astrochemical networks. The observed increase ink1at ca. 22 K does not significantly change the abundance of NH3in a typical cold dark interstellar cloud. However, the inclusion ofk2at ca. 22 K, not considered in astrochemical networks, indicates that the contribution of this destruction route for CH3NH2is not negligible, accounting for 1/3 of the assumed main depletion route (reaction with HCO+) in this IS environment.k1(OH+NH3)=(2.7±0.1)×10−11cm3s-1k2(OH+CH3NH2)=(3.9±0.1)×10−10cm3s-1

Electronic Energy and Local Property Errors at QTAIM Critical Points while Climbing Perdew's Ladder of Density-Functional Approximations.

We investigate the relationships between electron-density and electronic-energy errors produced by modern exchange-correlation density-functional approximations belonging to all of the rungs of Perdew's ladder. To this aim, a panel of relevant (semi)local properties evaluated at critical points of the electron-density field (as defined within the framework of Bader's atoms-in-molecules theory) are computed on a large selection of molecular systems involved in thermodynamic, kinetic, and noncovalent interaction chemical databases using density functionals developed in a nonempirical and minimally and highly parametrized fashion. The comparison of their density- and energy-based performance, also discussed in terms of density-driven errors, casts light on the strengths and weaknesses of the most recent and efficient density-functional approximations.

EnzymeML-a data exchange format for biocatalysis and enzymology.

EnzymeML is an XML-based data exchange format that supports the comprehensive documentation of enzymatic data by describing reaction conditions, time courses of substrate and product concentrations, the kinetic model, and the estimated kinetic constants. EnzymeML is based on the Systems Biology Markup Language, which was extended by implementing the STRENDA Guidelines. An EnzymeML document serves as a container to transfer data between experimental platforms, modeling tools, and databases. EnzymeML supports the scientific community by introducing a standardized data exchange format to make enzymatic data findable, accessible, interoperable, and reusable according to the FAIR data principles. An application programming interface in Python supports the integration of software tools for data acquisition, data analysis, and publication. The feasibility of a seamless data flow using EnzymeML is demonstrated by creating an EnzymeML document from a structured spreadsheet or from a STRENDA DB database entry, by kinetic modeling using the modeling platform COPASI, and by uploading to the enzymatic reaction kinetics database SABIO-RK.

Kinetics study of Pb evaporation from pure Pb and Pb–Ag alloy in vacuum evaporation process

Traditional method for treatment of Pb–Ag alloy has disadvantages of a long metal production cycle, long process, and high energy consumption. Vacuum distillation has obvious advantages, such as a short flow, short production cycle, high direct yields of metal, and low cost. Kinetics is the key factor that determines production efficiency. Therefore, evaporation kinetics of Pb evaporation from pure Pb and Pb–Ag alloy has been investigated. The evaporation rate of pure Pb was experimentally determined as 0.044, 0.13 and 0.32 g cm−2·min−1 at 1173 K, 1273 K and 1373 K, respectively. Pb evaporation from Pb–Ag alloy followed first order kinetics and the rate controlling step were mainly mass transfer in liquid which indicated that increasing the stirring of the melt during the production process can improve the removal efficiency of lead. In addition, some kinetic parameters were obtained such as the apparent activation energy of Pb evaporation from Pb–Ag alloy was 148.8 kJ mol−1, the mass transfer coefficient was 6.48 × 10−8, 1.90 × 10−7 and 6.00 × 10−7 m s−1 at 1173 K, 1273 K and 1373 K, respectively. The research enriches the Pb evaporation kinetic database and can provide theoretical guidance for the vacuum distillation of noble lead alloys. In addition, the research designs a set of alloy configuration and vacuum evaporation device with simple assembly and convenient operation which can be used for the research on vacuum evaporation kinetics of other non-ferrous metal alloy systems.

Automated assessment of a kinetic database for fcc Co–Cr–Fe–Mn–Ni high entropy alloys

The development of accurate kinetic databases by parametrizing the composition and temperature dependence of elemental atomic mobilities, is essential for correct multicomponent calculations and simulations. In this work the automated assessment procedure for the establishment of CALPHAD-type kinetic databases is proposed, including the storage of raw data and assessment results, automatic weighting of data, parameter selection and automated reassessments. This allows the establishment of reproducible up-to-date databases. The proposed software, written in python, is applied to the assessment of a kinetic database for the fcc Co–Cr–Fe–Mn–Ni high entropy alloy using only tracer diffusion data for a sharp separation of thermodynamic and kinetic data. The established database is valid for the whole composition range of the five-component high entropy alloy.

Multiphase-field simulation of austenite reversion in medium-Mn steels

Medium-Mn steels have attracted immense attention for automotive applications owing to their outstanding combination of high strength and superior ductility. This steel class is generally characterized by an ultrafine-grained duplex microstructure consisting of ferrite and a large amount of austenite. Such a unique microstructure is processed by intercritical annealing, where austenite reversion occurs in a fine martensitic matrix. In the present study, austenite reversion in a medium-Mn alloy was simulated by the multiphase-field approach using the commercial software MICRESS® coupled with the thermodynamic database TCFE8 and the kinetic database MOBFE2. In particular, a faceted anisotropy model was incorporated to replicate the lamellar morphology of reversed austenite. The simulated microstructural morphology and phase transformation kinetics (indicated by the amount of phase) concurred well with experimental observations by scanning electron microscopy and in situ synchrotron high-energy X-ray diffraction, respectively.

Phase field simulation of the stress-induced α microstructure in Ti–6Al–4 V alloy and its CPFEM properties evaluation

Variant selection under specific applied stresses during precipitation of α plates from prior-β matrix in Ti–6Al–4 V was investigated by 3D phase field simulations. The model incorporates the Burgers transformation path from β to α phase, with consideration of interfacial energy anisotropy, externally applied stresses and elastic interactions among α variants and β matrix. The Gibbs free energy and atomic mobility data are taken from available thermodynamic and kinetic databases. It was found that external stresses have a profound influence on variant selection, and the selection has a sensitive dependence, as evidenced by both interaction energy calculations and phase field simulations. Compared with normal stresses, shear stresses applied in certain directions were found more effective in accelerating the transformation, with a stronger preference to fewer variants. The volume fractions of various α variants and the final microstructure were determined by both the external stress and the elastic interaction among different variants. The α clusters formed by variants with Type2 misorientation ([1 1 -2 0]/60°) relation were found more favored than those with Type4 ([-10 5 5 -3]/63.26°) under certain applied tensile stress such as along <111>β. The mechanical properties of different microstructures from our phase field simulation under different conditions were calculated for different loading conditions, utilizing crystal plastic finite element simulation. The mechanical behavior of the various microstructures from phase field simulation can be evaluated well before the alloys are fabricated, and therefore it is possible to select microstructure for optimizing the mechanical properties of the alloy through thermomechanical processing based on the two types of simulations.

In-situ upgrading in a dolomite porous medium: A kinetic model comparison and nanocatalyst deposition study

Heavy oil extraction currently presents economic and environmental challenges due to low prices and costly energy usage for their exploitation and transport. The use of heavy oil as a sustainable source of energy requires novel and well-engineered technologies. In-Situ (in-reservoir) Upgrading Technology, ISUT, is an EOR-Upgrading process that combines the use of a hot dense fluid (i.e., vacuum distillation residue), hydrogen, and a nanocatalyst as upgrading agents. The operating control of this technology requires performance assessment and kinetic database for each application and each type of reservoir with specific rock-oil in place characteristics. In this work, a hydrocracking kinetic study is developed based on experiments carried out in a dolomite corepack using temperatures from 335 °C to 365 °C, residence times of 12 h–72 h under the constant pressure of 10 MPag, which are the typical ISUT's conditions for carbonate reservoirs. By using kinetic modeling, the operating temperatures were compared with a previous kinetic model, finding similar yields/reaction time performance results. Scanning Electron Microscopy (SEM) and Energy-Dispersive X-ray spectroscopy (EDX) techniques were used to analyze the nanocatalyst particles on the dolomite corepack's surface. The nanocatalysts deposited on the rock were in the range of 13 nm–1220 nm with two types, spherical- and agglomerated-shaped. The X-Ray Fluorescence Spectroscopy (XRF) was also used to determine metal content distributions along the corepack. Finally, ISUT's kinetic modeling studies so far, and this one, suggest the convenience of using the same model for the reservoirs studies, which include the effects of the conditions such as temperature, pressure or residence time used during ISUT's process application.

Automation of diffusion database development in multicomponent alloys from large number of experimental composition profiles

Nowadays, the urgency for the high-quality interdiffusion coefficients and atomic mobilities with quantified uncertainties in multicomponent/multi-principal element alloys, which are indispensable for comprehensive understanding of the diffusion-controlled processes during their preparation and service periods, is merging as a momentous trending in materials community. However, the traditional exploration approach for database development relies heavily on expertize and labor-intensive computation, and is thus intractable for complex systems. In this paper, we augmented the HitDIC (high-throughput determination of interdiffusion coefficients, https://hitdic.com) software into a computation framework for automatic and efficient extraction of interdiffusion coefficients and development of atomic mobility database directly from large number of experimental composition profiles. Such an efficient framework proceeds in a workflow of automation concerning techniques of data-cleaning, feature engineering, regularization, uncertainty quantification and parallelism, for sake of agilely establishing high-quality kinetic database for target alloy. Demonstration of the developed infrastructures was finally conducted in fcc CoCrFeMnNi high-entropy alloys with a dataset of 170 diffusion couples and 34,000 composition points for verifying their reliability and efficiency. Thorough investigation over the obtained kinetic descriptions indicated that the sluggish diffusion is merely unilateral interpretation over specific composition and temperature ranges affiliated to limited dataset. It is inferred that data-mining over large number of experimental data with the combinatorial infrastructures are superior to reveal extremely complex composition- and temperature-dependent thermal–physical properties.

Polyaniline dispersed by Kevlar fiber for uptake of organic dye

PurposeThis paper aims to focus on the preparation of Kevlar fiber (KF) and alkaline hydrolyzed KF (KF-H) to improve the dispersed condition of polyaniline (PAn), as the aggregation of PAn would lead to some adsorption sites buried. And then the materials were used to enrich anionic dye Congo red (CR) from aqueous solution.Design/methodology/approachThe materials (KF@PAn and KF-H@PAn) were designed by means of “diffusion-interfacial-polymerization” under mild condition as high affinity due to the structural properties of PAn, KF and KF-H. The dispersed degree of PAn on the surface of KF and KF-H was validated according to adsorption efficiency for CR.FindingsThe content of PAn introduced was not beyond 20 wt.%, while adsorption capacity for CR was significantly enhanced by 4–8 times (on the basis of kinetic data) according to the calculation only by the content of PAn due to KF and alkaline hydrolyzed KF exhibited almost no adsorption for CR, indicating dispersed situation of PAn coating was greatly enhanced and more active sites exposed, which was favorable for the adsorption process. Presence of NaCl would exhibit a more or less positive effect on CR uptake, suggesting the materials could be used for high salt environment.Research limitations/implicationsThe investigated means of dispersed degree of PAn on the surface of KF and KF-H are the further and future investigation.Practical implicationsThis study will provide a method to improve the dispersed situation of PAn and a theoretical support to treat anionic dyes from aqueous solution especially for salt environment.Originality/valueThe results showed that the dispersed condition of PAn on the surface of KF and KF-H was greatly improved. According to the adsorption capacities for CR, it can be concluded that part of adsorption sites were buried due to the aggregation of PAn, and introduction of KF and KF-H, buried adsorption sites decreased greatly. This study will provide a method to decrease buried adsorption sites of PAn and a contribution for their convenient application in wastewater treatment especially for high salt environment.

Reducing hot tearing by grain boundary segregation engineering in additive manufacturing: example of an AlxCoCrFeNi high-entropy alloy

One major hindrance that alloy design for additive manufacturing (AM) faces nowadays is hot tearing. Contrary to the previous works which either try to reduce solidification range or introduce grain refinement, the current work presents a new approach of employing segregation engineering to alter the residual stress states at the interdendritic and grain boundary regions and consequently prevent hot tearing. Here, in situ Al alloying is introduced into an existing hot-cracking susceptible high-entropy alloy CoCrFeNi. It is found that within a certain range of compositions, such as Al0.5CoCrFeNi, the hot crack density was drastically decreased. During the solidification of this specific alloy composition, Al is firstly ejected from the primary dendritic face-centred cubic (FCC) phase and segregates into the interdendritic regions. Spinodal decomposition then occurs in these Al-enriched regions to form the ordered B2 NiAl and disordered body-centred cubic (BCC) Cr phases. Due to the higher molar volume and lower homologous temperatures of these B2/BCC phases, the inherent residual strain is accommodated and transformed from a maximum 0.006 tensile strain in CoCrFeNi to a compressive strain of ~0.001 in Al0.5CoCrFeNi. It is believed that this grain boundary segregation engineering method could provide a new pathway to systematically counteract the hot tearing problem in additive manufacturing of metals and alloys, using available thermodynamic and kinetic database information.

Towards a high-accuracy kinetic database informed by theoretical and experimental data: CH3 + HO2 as a case study

The reliability of predictive simulations for advanced combustion engines depends on the availability of accurate data and models for thermochemistry, chemical kinetics, and transport. In that regard, accurate data are critically important for both their direct use in predictive simulations and for benchmarking improved theoretical methodologies that can similarly produce accurate data for predictive simulations. The use of informatics-based strategies for the determination of accurate thermochemical data with well-defined uncertainties, e.g. the Active Thermochemical Tables (ATcT), has revolutionized the field of thermochemistry–providing thermochemical data of unprecedented accuracy for predictive combustion simulations and has served as a key enabler of ab initio electronic structure methodologies of equally impressive accuracy. Clearly, pursuit of informatics-based analogs in chemical kinetics would be similarly worthwhile. Here, we present results and analyses for the kinetics of CH3 + HO2 reactions that demonstrate some key elements of any approach to developing analogs for kinetics, including: the importance of raw data for quantifying the information content of experimental data, the utility of theoretical kinetics calculations for constraining experimental interpretations and providing an independent data source, and the subtleties of target data selection for avoiding unphysical parameter adjustments to match data affected by structural uncertainties. Notably, we find the optimization performed here using the MultiScale Informatics (MSI) approach applied to carefully selected (mostly raw) experimental data yields an opposite temperature dependence for the channel-specific CH3 + HO2 rate constants as compared to a previous rate-parameter optimization. While both optimization studies use the same theoretical calculations to constrain model parameters, only the present optimization, which incorporates theory directly into the model structure, yields results that are consistent with theoretical calculations.

Organic geochemistry and basin modeling of Late Cretaceous Harshiyat Formation in the onshore and offshore basins in Yemen: Implications for effective source rock potential and hydrocarbon generation

The purpose of this study is to present the source rock characteristics of Late Cretaceous Harshiyat Formation source rock in the onshore and offshore basins of Yemen (i.e. Mukalla-Sayhut, Sayun–Masilah , and Jiza-Qamar). Source rock geochemical characterizations were completed and integrated to perform 1-D basin modeling to back-predict source rock thermal maturation, oil generation and expulsion.The geochemical findings revealed that mudstone intervals within the Harshiyat Formation comprised favorable source rocks, with total organic carbon (TOC) content between 0.50 and 35.10 wt %. The organic matter intervals in the Harshiyat mudstones are mainly Types II/III and III kerogens, with certain amount of Type II and I kerogens based on Rock-Eval HI values, ranging from 40 to 923 mg HC/g TOC. Mixed kerogen types were consistent with vitrinite and sapropelic organic matters, as observed by visual kerogen examination and the distribution of biomarker fingerprints. The existence of mixed types I, II, and III organic matter suggests that the Harshiyat mudstones could contribute to oil and gas at sufficient thermal maturity levels. The biomarker data of the organic matter in the Harshiyat mudstones show that the source rock contains a mix marine phytoplanktonic-bacteria/terrestrial land plant enthronement and were deposited in suboxic-anoxic conditions.Results of chemical and optical maturity indicators led to the conclusion of varying maturity stages from immature to late oil window levels for the mudstones of the Harshiyat Formation. Thermal maturation distributions inferred from the analyzed samples indicate that mudstone intervals in the offshore Mukalla-Sayhut Basin are extremely mature, compatible with the late-mature oil window and may have generated significant amounts of oil. This interpretation was supported by strong geochemical similarity between the organic matter in the mudstones and those of the oils found in the offshore Mukalla-Sayhut Basin and demonstrated by the concentrations of n-alkanes and isoprenoids as well as carbon isotopes.In the offshore Ras-Ghashwah-1X well, burial and thermal models were constructed and used to address the effect of tectonic events in triggering oil generation and expulsion from mature Harshiyat source rock in the offshore area. Kinetic database models for Type II and III kerogen mixtures indicate that the initial conversion of kerogen to oil occurred since the Late Oligocene with transformation ratios (TR) that span between 10% and 50%. Furthermore, the oil was expelled from organic matter intervals in the Harshiyat source rock starting from Late Oligocene and continuing until Late Miocene, with TRs of 50%–72%. From that period up to the present, the retained oil was cracked into wet gas in the gas window with an Easy %Ro greater than 1.30, and with peak TR ratios greater than 72%.

Thermodynamic assessment of the Ni–Co–Cr system and Diffusion Study of its fcc phase

In the present work, the liquidus and solidus for a series of NixCo1-2xCrx alloys were measured by means of differential scanning calorimetry, and the first-principles calculations were performed to obtain total energies for all solid solutions and end-members of the intermediate phases in the Ni–Co–Cr ternary system. Various types of data from the present work and the literature were used in the assessments of the Ni–Co–Cr ternary system and sub-binary systems by the CALPHAD method, and were well reproduced by the present thermodynamic database. In addition, diffusion couples of fcc Co–Cr and Ni–Co–Cr alloys were assembled and annealed at different temperatures to extract interdiffusion coefficients. Experimental diffusion data from the present work and the literature, in conjunction with thermodynamic parameters, were adopted to assess the atomic mobilities of the fcc phase in the Ni–Co–Cr system. The calculated and experimental diffusion coefficients reach a satisfactory agreement. The diffusional kinetic database developed was further validated by appropriate predictions of composition profiles and diffusion paths.

MgC6H2 Isomers: Potential Candidates for Laboratory and Radioastronomical Studies.

Eighty three stationary points of MgC6H2 isomers spanning from 0 to 215 kcal mol-1 have been theoretically identified using density functional theory at the B3LYP/6-311++G(2d,2p) level of theory. Among them, four low-lying isomers lying within 23.06 kcal mol-1 (1 eV) have been further characterized in detail using high-level coupled-cluster (CC) methods. The thermodynamically most stable isomer turns out to be 1-magnesacyclohepta-4-en-2,6-diyne (1). The other three isomers, 3-magnesahepta-1,4,6-triyne (2), 1-magnesacyclohepta-2,3,4-trien-6-yne (3), and 1-magnesahepta-2,4,6-triyne (4) lie 8.24, 19.76, and 21.36 kcal mol-1, respectively, above 1 at the ae-CCSD(T)/cc-pCVTZ level of theory. All the four isomers are polar with a permanent electric dipole moment (μ ≠ 0). Hence, they are potential candidates for rotational spectroscopic studies. Considering the recent identification of magnesium-bearing hydrocarbons such as, MgC2H and MgC4H in IRC+10216, it is believed that the current theoretical data may be of relevance to laboratory molecular spectroscopic and radioastronomical studies on MgC6H2 isomers. The energetic and spectroscopic information gathered in this study would aid the detection of low-lying MgC6H2 isomers in the laboratory, which are indispensable for radioastronomical studies. It is also noted here that neither the National Institute of Standards and Technology Chemistry WebBook nor the Kinetic Database for Astrochemistry lists any isomer of MgC6H2 at the moment. Therefore, these isomers are studied here theoretically for the very first time.

Breakdown curves of CH2(+), CH3(+), and CH4(+) molecules

Aims. The aim of this work is to provide semi-empirical branching ratios (BRs) for the kinetic databases used in astrochemistry, such as the KInetic Database for Astrochemistry (KIDA). Our work focuses on the CHy(+) species (y = 2–4) excited by cosmic rays (CR), electrons, and photons (UV), or the intermediate excited complexes CHy(+) resulting from chemical reactions. It also intends to test the sensitivity of benchmark calculations to those new physical inputs in cold quiescent clouds and in photo-dissociation regions (PDRs). Methods. We constructed semi-empirical breakdown curves (BDCs) based on the collision of CHy+ (y = 2–4) projectiles of constant velocity (250 keV uma−1) with He atoms as explained in a previous paper, where BRs for UV, CR, and electronic processing were also derived. The same BDCs were applied to predict BRs for chemical reactions (bi-molecular neutral and ionic reactions, charge exchange). The effect of the new BRs on the chemical composition of cold dark clouds was tested using the time-dependent Nautilus gas-grain model. The same effect on the chemical composition of PDRs was tested using the Meudon PDR code. Results. Branching ratio predictions of the model are found to be in good agreement with available BR measurements for charge exchange reactions and the reaction between C and H3+. The chemistry for both cold clouds and PDRs is found to be not strongly affected by this update of BRs.

State-to-State Master Equation and Direct Molecular Simulation Study of Energy Transfer and Dissociation for the N2-N System.

We present a detailed comparison of two high-fidelity approaches for simulating non-equilibrium chemical processes in gases: the state-to-state master equation (StS-ME) and the direct molecular simulation (DMS) methods. The former is a deterministic method, which relies on the pre-computed kinetic database for the N2-N system based on the NASA Ames ab initio potential energy surface (PES) to describe the evolution of the molecules' internal energy states through a system of master equations. The latter is a stochastic interpretation of molecular dynamics relying exclusively on the same ab initio PES. It directly tracks the microscopic gas state through a particle ensemble undergoing a sequence of collisions. We study a mixture of nitrogen molecules and atoms forced into strong thermochemical non-equilibrium by sudden exposure of rovibrationally cold gas to a high-temperature heat bath. We observe excellent agreement between the DMS and StS-ME predictions for the transfer rates of translational into rotational and vibrational energy, as well as of dissociation rates across a wide range of temperatures. Both methods agree down to the microscopic scale, where they predict the same non-Boltzmann population distributions during quasi-steady-state dissociation. Beyond establishing the equivalence of both methods, this cross-validation helped in reinterpreting the NASA Ames kinetic database and resolve discrepancies observed in prior studies. The close agreement found between the StS-ME and DMS methods, whose sole model inputs are the PESs, lends confidence to their use as benchmark tools for studying high-temperature air chemistry.