Rate Coefficients Research Articles

Measurements and simulations of rate coefficients for the deuterated forms of the H2+ + H2 and H3+ + H2 reactive systems at low temperature

Measurements and simulations of rate coefficients for the deuterated forms of the H2+ + H2 and H3+ + H2 reactive systems at low temperature

Quantum rotational dynamics of linear C5 at low interstellar temperatures for H2 collision.

The quantum dynamics of carbon chains through H2 and He collisions in the interstellar medium (ISM) is an important step toward accurate modeling of their abundance in non-local thermodynamic equilibrium conditions. The C5(Σg+1) molecule is the longest pure carbon chain detected in the ISM to date. While He collisions are computationally easy to perform, the collision with much more abundant H2 is both complicated and computationally demanding. Using templates for approximating p-H2 collisional rates, such as scaling He rates and using a reduced 4D → 2D potential energy surface (PES), has limited applicability. On the other hand, any such approximation does not exist for o-H2. Therefore, a full rotational dynamics of C5 with both p- and o-H2 is performed considering both molecules as rigid-rotors. The PES is calculated using CCSD(T)-F12a/AVTZ, and a neural network fitting model has been carefully chosen to strictly obey spectroscopic accuracy and augment the PES. The augmented PES is then expanded into radial terms using the bispherical harmonics function, and close coupling calculations have been done to get the cross sections and, subsequently, rate coefficients for various rotational transitions of C5.

Bimolecular kinetics of Criegee intermediate (CH2OO) with 2-pentanone: experimental and theoretical analysis in atmospheric conditions.

Temperature-dependent kinetics of Criegee intermediate (CH2OO) with 2-pentanone were performed at 258-318 K and 50 Torr using pulsed laser photolysis-cavity ring-down spectroscopy (PLP-CRDS) technique. The measured room temperature rate coefficient was (3.84 ± 0.24) × 10-13 cm3 molecule-1 s-1. The reaction follows a negative temperature dependency, and the corresponding Arrhenius equation is k4 = (1.76 ± 0.36) × 10-15exp{(3.18 ± 0.11) kcal mol-1/RT}. The high-P limit rate coefficients obtained using CVT/SCT at CCSD(T)/aug-cc-pVTZ//B3LYP/6-311 + G(2df,2p) level of theory deviate from the experimental results, especially in the low-temperature region. At 258 K, the computed high-P limit rate coefficient exceeded the experimental value by more than a factor of four. Comparing all the reaction pathways, HCOOH was the major product formed in the title reaction. The atmospheric lifetime of 2-pentanone due to its reaction with CH2OO was calculated to be ~ 3000 days, rendering the reaction insignificant for inclusion in models of atmospheric 2-pentanone.

Studies of electron-ion resonant recombination of li-like Si11+ions

Abstract Theoretical investigations of L-shell △n = 0, 1, and 2 (2s → 2p, 3 l ′ , and 4 l ′ ) dielectronic recombination (DR), as well as K-shell △n = 1, 2, and 3 (1s → 2 l ′ , 3 l ′ , and 4 l ′ ) DR of Li-like Si 11+ ions are performed, using the relativistic distorted-wave approach. Detailed resonance energies, resonance strengths, and recombination rate coefficients are calculated including complex configuration mixing, Breit interaction, and QED corrections. Good agreement is achieved between the theoretical rate coefficients and the experimental results. The plasma rate coefficients are also calculated for electron temperatures ranging from 10−1 to 106 eV, and an analytical formula is presented to fit the total plasma rate coefficients for convenient modeling of astrophysical and fusion plasmas.

A Study of Downlink Power-Domain Non-Orthogonal Multiple Access Performance in Tactile Internet Employing Sensors and Actuators

The Tactile Internet (TI) characterises the transformative paradigm that aims to support real-time control and haptic communication between humans and machines, heavily relying on a dense network of sensors and actuators. Non-Orthogonal Multiple Access (NOMA) is a promising enabler of TI that enhances interactions between sensors and actuators, which are collectively considered as users, and thus supports multiple users simultaneously in sharing the same Resource Block (RB), consequently offering remarkable improvements in spectral efficiency and latency. This article proposes a novel downlink power domain Single-Input Single-Output (SISO) NOMA communication scenario for TI by considering multiple users and a base station. The Signal-to-Interference Noise Ratio (SINR), sum rate and fair Power Allocation (PA) coefficients are mathematically derived in the SISO-NOMA system model. The simulations are performed with two-user and three-user scenarios to evaluate the system performance in terms of Bit Error Rate (BER), sum rate and latency between SISO-NOMA and traditional Orthogonal Multiple Access (OMA) schemes. Moreover, outage probability is analysed with varying fixed Power Allocation (PA) coefficients in the SISO-NOMA scheme. In addition, we present the outage probability, sum rate and latency analyses for fixed and derived fair PA coefficients, thus promoting dynamic PA and user fairness by efficiently utilising the available spectrum. Finally, the performance of 4 × 4 Multiple-Input Multiple-Output (MIMO) NOMA incorporating zero forcing-based beamforming and a round-robin scheduling process is compared and analysed with SISO-NOMA in terms of achievable sum rate and latency.

Semiclassical Transition State Theory (SCTST) Rate Coefficients for the Unimolecular Decomposition of the Ethoxy (CH3CH2O) Radical.

The thermal unimolecular decay of ethoxy is important in high-temperature combustion environments where the ethoxy radical is a key reactive intermediate. Two dissociation pathways of ethoxy, including the β-C-C scission to yield CH3 + CH2O and the H-elimination to make H + CH3CHO, were characterized using a high-level coupled-cluster-based composite quantum chemical method (mHEAT-345(QΛ)). The former route is found to be dominant while the latter is insignificant, in agreement with previous experimental and theoretical studies. Thermal rate coefficients are calculated for P = 0.001-658 atm (of air) and T = 300-2500 K using semiclassical transition state theory (SCTST) in combination with a pragmatic two-dimensional E,J-resolved master equation (2DME). The effects of tunneling and anharmonicity on the calculated rate constants are also examined. The tunneling factor is found to be inversely dependent on pressure, contrary to previous observations of pressure-dependent tunneling in entrance channels.

Enhancement of the Reinforcement Effect of Calcium Carbonate or Silica on Natural Rubber Using Lauryl Alcohol

Calcium carbonate (CaCO3) and silica are two types of additives for rubber. Through the implementation of a typical semi-efficient (Semi-EV) vulcanisation formulation, those additives were added separately into the compound of natural rubber (NR). The CaCO3 or silica was added as the reinforcing filler and, incorporated into NR at a constant concentration i.e., 30 parts per hundred NR (phr). It was found that the CaCO3 or silica have successfully provided an increase in mechanical properties including a greater tensibility (tensile strength) and abrasion resistance of the compound of NR. However, as hydrophilic fillers, the CaCO3 or silica is hard to disperse homogeneously and hence, lauryl alcohol was used to improve their dispersion degrees. It was combined into the NR compound with varied concentrations such as 1, 3, 5 and 7 phr. Therefore, the effect of lauryl alcohol concentration on the processing and reinforcement properties of CaCO3 or silica-filled NR was investigated. It could be found that lauryl alcohol has increased the rate coefficient of vulcanisation (Rv) of the CaCO3 or silica-filled-NR. The greater the lauryl alcohol concentration; the greater the Rv value, tensile strength, and abrasion resistance. Overall, lauryl alcohol has a successful function as a plasticizing agent which increased the reinforcement effects of the fillers on NR through the increasing of crosslink density of CaCO3-NR or silica-NR especially at the 5 phr of addition.

Rate coefficients for C and O2 reactive collisions relevant to interstellar clouds from QCT and machine learning.

The chemical reactions between certain interstellar molecules are exothermic in nature and barrierless in the entrance channel, allowing these reactions to occur rapidly even at low astronomical temperatures, e.g., C and O2 interaction. Obtaining detailed rovibrational transition parameters for the reaction between C and O2, such as state-selected rate coefficients, is crucial for studying the associated atmospheric and astronomical environments. Hence, this work presents an approach that combines quasi-classical trajectory calculations with machine learning techniques based on Neural Network (NN) and Gaussian Process Regression (GPR) to determine state-selected rate coefficients. Employing this approach, we significantly reduced the computational requirements while simultaneously obtaining the accurate state-selected reaction cross sections and rate coefficients for the collision of C and O2. Both the NN-based and GPR-based models established in this work accurately predict the results calculated from explicit numerical calculations in the explored temperature range of 50-1500K, achieving a coefficient of determination R2 > 0.96. Most importantly, the current work provides the most comprehensive dataset of rovibrational rate coefficients of v = 0-4, j = 0-70 → v' = 0-15 for the astrophysical modeling of the C-O2 collision system.

Trade-Off Between Wear/Corrosion Performance and Mechanical Properties in D-AlNiCo Poly-Quasicrystals Through CNT Addition to the Microstructure

An ultrafine-grained Al71Ni14.5Co14.5/CNT poly-quasicrystal (QC/CNT) composite was synthesized using spark plasma sintering of powder components developed through electroless Ni-P/CNT plating of Co particles and mechanical alloying. The performance of the synthesized samples was studied using various testing methods, such as room temperature/hot compression, wear, and corrosion tests. The results were compared to the properties of alloy samples fabricated from raw and coated powders (without CNTs). The wear rate and friction coefficient of the quasicrystalline samples improved significantly due to the contribution of the CNTs. The wear rate of the CNT-containing specimens was 0.992 × 10−4 mm3/N/m, which is 47.1% lower than that of the QC sample. The positive impact of the CNTs on the corrosion potential and current density was further validated by the potentiodynamic polarization tests in a saline solution. However, these improvements in surface properties came at the cost of a 21.5% reduction in compressive strength, although the compressive strength still remained above 1.1 GPa at 600 °C. The results highlight an interesting trade-off between surface properties and mechanical strength, pointing toward the development of materials suitable for extreme conditions.

Approximating families of sharp solutions to Fisher's equation with physics-informed neural networks

This paper employs physics-informed neural networks (PINNs) to solve Fisher's equation, a fundamental reaction-diffusion system with both simplicity and significance. The focus is on investigating Fisher's equation under conditions of large reaction rate coefficients, where solutions exhibit steep traveling waves that often present challenges for traditional numerical methods. To address these challenges, a residual weighting scheme is introduced in the network training to mitigate the difficulties associated with standard PINN approaches. Additionally, a specialized network architecture designed to capture traveling wave solutions is explored. The paper also assesses the ability of PINNs to approximate a family of solutions by generalizing across multiple reaction rate coefficients. The proposed method demonstrates high effectiveness in solving Fisher's equation with large reaction rate coefficients and shows promise for meshfree solutions of generalized reaction-diffusion systems.

Ion Size, Electron Rate and Transfer Coefficient Effect on Hetrocharge Redox Couple (+1,0) for 2‐D Microdisk, Potential Application for Lithium Ion Battery

AbstractNumerical finite element simulations were conducted to study the electrochemical reaction in a mixture of hetrocharge redox couple in the presence of a supporting electrolyte as a potential application in lithium ion battery, occurring on both parallel and non‐parallel two dimensional (2‐D) microdisk electrodes. Ion size of supporting electrolyte and electron transfer rate by engineering of electrode types have significant effect on electrical storage. This study represents the first‐time exploration of the electrochemical behavior for hetrocharge +1,0 redox couple in presence of supporting electrolyte on a non‐parallel 2D microdisk. Impedance spectra were calculated for the electrochemical reaction on the non‐parallel 2D microdisk under varying concentrations of the redox couple and supporting electrolyte. COMSOL simulation were extended to investigate the effects of electron rate and transfer number on the Impedance spectrum, as well as the concentration of all ions and electrical potential within the electrical double layer area for the 2‐D microdisk. Analytical expressions were derived to describe the potential and concentration profiles in the double layer area, specifically for the electrochemical reaction involving hetrocharge redox couple +1, 0 on a 2‐D parallel microdisk in the presence of the supporting electrolyte. The study explored the influence of different types of supporting electrolytes, namely KF and KBr, on the impedance spectrum, concentration profile, and electrical potential profile within the electrical double layer area for the non‐parallel 2‐D microdisk. General trend of numerical impedance spectrum result with the ion size of supporting electrolyte is agreement with the available experimental data.

Inelastic Triatom-Atom Quantum Close-Coupling Dynamics in Full Dimensionality: All Rovibrational Mode Quenching of Water Due to the H Impact on a Six-Dimensional Potential Energy Surface.

The rovibrational level populations, and subsequent emission in various astrophysical environments, are driven by inelastic collision processes. The available rovibrational rate coefficients for water have been calculated using a number of approximations. We present a numerically exact calculation for the rovibrational quenching for all water vibrational modes due to collisions with atomic hydrogen. The scattering theory implements a quantum close-coupling (CC) method on a high level ab initio six-dimensional (6D) potential energy surface (PES). Total rovibrational quenching cross sections for excited bending levels were compared with earlier results on a 4D PES with the rigid-bender close-coupling (RBCC) approximation. General agreement between 6D-CC and 4D-RBCC calculations are found, but differences are evident including the energy and amplitude of low-energy orbiting resonances. Quenching cross sections from the symmetric and asymmetric stretch modes are provided for the first time. The current 6D-CC calculation provides accurate inelastic data needed for astrophysical modeling.

Emission of high rovibrational hydrogen molecules under detached plasma conditions by recycling on the tungsten wall

Abstract It is well known that the rate coefficient of molecular-assisted recombination (MAR) varies by several orders of magnitude depending on the rovibrational states of the hydrogen molecules. A molecular dynamics simulation is performed to estimate the rovibrational states of recycled hydrogen molecules at the divertor in the JA-DEMO reactor under detached plasma conditions. The simulation results reveal that molecules in high rovibrational states are released even with low incident energy, which will be the dominant condition under detached plasma conditions. Molecules generated in this way can strongly affect the formation of the detached plasma via a molecular assisted-process such as MAR.

Kinetic models for the methanation of COx gases to produce methane: A critical analysis

An exhaustive review of the available literature regarding the kinetic models for the methanation of COx gases to produce natural gas (CH4) is reported. Since the oldest and recent reported kinetic studies about this topic were discussed and analyzed. The characteristics of the experimental studies such as the reaction system, operating conditions, catalyst used, and the experimental procedure, as well as the derived reaction rate equations, reaction rate coefficients and activation energies are highlighted. The results of the various kinetic models are also discussed in order to identify appropriate approaches that can be used as reference to develop new kinetic models. Most of the works reported values of reaction order of 0.2–1 and activation energies of 75–110 kJ/mol in a temperature range of 220–450 °C. Average absolute error (ε) values were calculated to evaluate the accuracy of the predicted data, which resulted to be in the range of 0.15 %–8.08 % showing generally a good agreement.

Introducing a prediction method for the photodegradation of p-cresol, a phenolic contaminant of emerging concern, in wastewater effluent

Despite extensive efforts to understand the photodegradation of phenolic contaminants of emerging concern (PhCECs) in aquatic systems, prediction methods, especially in waters containing effluent organic matter (EfOM), remain underdeveloped. This study introduces a prediction method for p-cresol, a representative PhCECs, based on correlations between EfOM optical parameters and p-cresol kinetic parameters. We examined p-cresol photodegradation in various EfOM samples, characterized by their optical properties, and used the reaction rate coefficient between EfOM and p-cresol, α3EfOM⁎, to quantify and predict p-cresol degradation in different wastewater effluent samples. Results showed significant correlations between p-cresol's photodegradation rate constant (0.144 to 0.441 h−1) and EfOM characteristics, with α3EfOM⁎ values ranging from 4 × 1011 to 10 × 1011 M−1 s−1. The method was validated with p-cresol at concentrations ranging from 25 to 100 μM and multiple EfOM samples. The method's applicability was further evaluated using propranolol, a pharmaceutical contaminant of emerging concern, demonstrating its versatility for predicting the degradation behavior of other contaminants in different wastewater samples. The method accurately predicted p-cresol and propranolol degradation across diverse wastewater samples, suggesting its potential for expansion to other classes of contaminants, aiding in water quality management, improving wastewater treatment processes, and enhancing environmental risk assessments.

Measurements of the Reaction Rate Coefficients of Atomic Hydrogen with Astrochemical Anions: CN− and C3N−

We present the temperature-dependent reaction rate coefficients of CN− and C3N− with atomic hydrogen in the temperature range from 7 to 290 K, measured in a 16-pole radio-frequency ion trap. The rate of C3N− with H steadily increases toward lower temperatures, while the rate coefficients for the CN− + H system show a sudden change around 160 K. Fits to the data were performed to determine temperature-dependent reaction rate coefficients. The fits reveal a rate coefficient of 4.1(3)×10−10(T/300)−0.31(6) cm3 s−1 for C3N− + H. For CN−, we determined a rate coefficient for the temperature regime below 160 K of 3.2(4)×10−10(T/300)−0.31(11) cm3 s−1. Given our present results, higher rate coefficients than previously reported must be assumed for the modeling of cold interstellar environments involving these H atom reactions.

Benchmarking Dielectronic Recombination Rate Coefficients for Carbon-like Ca14+

Dielectronic recombination (DR) rate coefficients for C-like Ca14+ were measured by Wen et al. at the electron cooler storage ring in Lanzhou, China. The measured DR rate coefficients from 0 to 92 eV cover most of the DR resonances associated with the 2s 22p 2 → 2s 22p 2 and 2s 22p 2 → 2s2p 3 core transitions. In addition, Wen et al. reported theoretical results calculated with the Flexible Atomic Code (FAC) and AUTOSTRUCTURE (AS). However, these theoretical results show widespread and significant differences from the measured DR spectrum in both resonance energies and strengths, as well as between each other. In the present work, we uncover the reasons behind these large differences, both theoretical and experimental. The new FAC and AS results reproduce the observed spectrum in detail, especially at resonance energies below 8 eV, and they are in very close agreement with each other. The present plasma rate coefficients agree with the experimentally determined values to within 20% and 2% in the photoionized plasma (PP) and collisional ionized plasma (CP) temperature ranges, respectively. This is in contrast to the previous theoretical results, which showed differences with the experiment of up to ∼40% over the PP temperature range. The present FAC and AS results agree with each other within 5% in the PP and CP temperature ranges. Thus, the theoretical uncertainty is greatly reduced for the DR of Ca14+ and the present benchmarking with the experiment gives confidence to data users modeling non–local thermodynamic equilibrium plasma.

Zero-dimensional simulations of DC ns-pulsed plasma jet in N2 at near atmospheric pressure: validation of the vibrational kinetics

Abstract A Direct Current (DC) nanosecond (ns)-pulsed plasma jet fed with N2 at near atmospheric pressure (20 000 Pa) is studied using a transient zero-dimensional (0-D) model coupled with a two-term Boltzmann equation solver. Good agreement is observed between the simulated and measured plasma properties: including the electron density and the ratios of the N2(v = 1, 2, 3, 4) densities to the gas density. A variety of theoretical approaches are considered to determine the Vibrational-Vibrational (V-V) and Vibrational-Translational (V-T) rate coefficients. For the V-V kinetics, the simple form of an Harmonic Oscillator (sfHO), the Schwartz–Slawsky–Herzfeld (SSH) and the Forced Harmonic Oscillator (FHO) approaches are used. The SSH approach used in this study is an improved version based on the pure SSH approach. For the V-T kinetics, the sfHO, a fit function of the Semi-Classical (ffSC) calculations and a fit function of the Quasi-Classical Trajectory (ffQCT) calculations are used. The influence of these different approaches on the calculated temporal evolution profiles of the vibrational distribution functions (VDFs) within one pulse modulation cycle is revealed. It is observed that the use of these different approaches does not strongly affect the densities of the low vibrational levels (v < 5), whereas larger influences on the higher level densities are found. In addition, it is found that the simulated evolution of the VDFs are sensitive to the probabilities of the neutral wall reaction N2(v) + wall → N2(v − 1) in the range of 1 × 10−2 to 1 × 10−4. A further analysis of the wall quenching probabilities of N2(0 < v < 58) is of importance for a more accurate prediction of the VDFs.

Effect of B/N dual doping on mechanical and tribological properties of Mo-S-B-N sputtered films

Doping with non-metal element is effective to improve the porous morphology and enhance the mechanical and tribological properties of transition metal dichalcogenides (TMDs) based film. However, the mechanical properties of TMDs based film with single additive should be enhanced further for better wear resistance. In this work, B/N dual-doping was used to further enhance the deformation resistance and toughness of MoS2 based films deposited by magnetron sputtering, while the effect of B/N dopants on the structure, mechanical and tribological properties has been investigated. Mo-S-B-N film with B content of 20.91 at. % and N content of 18.13 at. % consists of MoS2 and amorphous nitride/boride, in which B/N dual doping film forms a higher ordered MoS2 lamellar structure compared to B doping film. With a hardness of 11.6±0.9 GPa and improved toughness, the film achieves a low wear rate and average friction coefficient is achieved. Comparing B/N dual doping film to B doping film, the stable formation of tribolayer with more strengthened deformation resistance results in the steady friction and the improved wear resistance, while the limited TMDs reorientation leads to the slight increase of friction coefficient.

Influence of nanodiamond on compressive and dry-sliding wear behaviors of Al2O3–Al interpenetrating-phase composites

In this research, the effects of nanodiamond (ND) addition at different loadings on the compressive and wear properties of the interpenetrating phases hybrid aluminum/alumina (Al/Al2O3) composite were investigated. The samples were fabricated in a two-step process. First, the Al2O3-ND preforms were fabricated via the replica method. Second, the squeeze casting route was employed to infiltrate the molten pure Al. The ceramic preforms were made by immersing a polyurethane foam with 17 ppi pores in a slurry containing α-Al2O3 powder (1 μm), ND particles (0–10 vol%), and natural egg white. After sintering at 1500 °C for 4 h, the preheated preforms were infiltrated with molten Al. The microstructural evaluations of the preforms and composites revealed a proper distribution of the ND particles in the preform, as well as the formation of the ND agglomerates at higher volume percentages. Also, the hardness of the samples enhanced with an increase in the ND loading, reaching a maximum of 263.8 Vickers for the 10 vol% ND-loaded composite. The compressive strength of the samples enhanced up to 3 vol% ND addition and then decreased due to the agglomeration. The wear test results indicated that the best behavior was related to the 3 vol% ND-loaded composite. Embedding the 3 vol% ND decreased the weight rate and friction coefficient of the interpenetrating phases hybrid Al/Al2O3 composite by 16 % (from 8.2396×10−3 to 6.9269×10−3 mm3/m) and 12 % (0.8165 to 0.7238), respectively. The study of the worn surfaces of the samples after wear testing revealed that the dominant wear mechanisms were abrasive and adhesive for the higher and lower volume fractions of the ND, respectively.