Thermal Rate Constants Research Articles

Reactive Rate Constants for the C+ + H2(v = 0, 1) Reaction: An Accurate State-to-state Quantum Dynamical Study

Abstract The accurately calculated thermal rate constants of the C+ + H2(v = 0, 1) reaction are important for estimating the CH+ emission spectra in different astronomical environments. In this study, reactive quantum dynamics of the C+ + H2(v = 0, 1) reaction have been investigated with the time-dependent wave packet method on the high-quality potential energy surface recently developed by Guo et al. The simulated total cross sections are compared in detail with previous experimental measurements and dynamical results. The calculated total rate constants are found to be in good agreement with previous quasi-classical results by Herráez-Aguilar et al., except for the v = 0 reaction at low temperatures. The ro-vibrational state-resolved rate constants show that the CH+ product, obtained from both the v = 0 and v = 1 reactions, is significantly populated in the vibrational ground but rotational excited states. In particular, for the v = 0 reaction, the CH+ product is preferably formed at j′ = 4, 5 rotational levels, while the CH+ product for the v = 1 reaction prefers rotational excitation j′ = 6–8. This finding varies with previous J-shifting calculations by Zanchet et al., owing to the different potential energy surface and methodology employed in the calculations.

Helium Isotopes Quantum Sieving through Graphtriyne Membranes.

We report accurate quantum calculations of the sieving of Helium atoms by two-dimensional (2D) graphtriyne layers with a new interaction potential. Thermal rate constants and permeances in an ample temperature range are computed and compared for both Helium isotopes. With a pore larger than graphdiyne, the most common member of the -graphyne family, it could be expected that the appearance of quantum effects were more limited. We find, however, a strong quantum behavior that can be attributed to the presence of selective adsorption resonances, with a pronounced effect in the low temperature regime. This effect leads to the appearance of some selectivity at very low temperatures and the possibility for the heavier isotope to cross the membrane more efficiently than the lighter, contrarily to what happened with graphdiyne membranes, where the sieving at low energy is predominantly ruled by quantum tunneling. The use of more approximate methods could be not advisable in these situations and prototypical transition state theory treatments might lead to large errors.

Catalytic effect of solvothermally prepared Cu2(bdc)2(bpy) metal-organic framework on thermal decomposition of ammonium perchlorate

Cu2(bdc)2 (bpy) metal-organic framework (MOF) was prepared by solvothermal method and the structure was characterized by powder X-ray diffraction (PXRD), scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT-IR). The specific surface area and the pore size distributions was estimated by Brunauer–Emmett–Teller (BET) method and micropore (MP) plot. This metal-organic framework was used as catalyst to improve the thermal decomposition of ammonium perchlorate (AP) and thermal behaviors of the mixed samples containing the catalyst and ammonium perchlorate were investigated by thermogravimetric analysis (TGA) and differential scanning calorimetric (DSC) experiments. The results showed that in the catalyzed samples, the heat released from thermal decomposition of ammonium perchlorate is much higher (more than 3 times in sample containing 4% by weight of the metal-organic framework as catalyst) and thermal decomposition temperature was significantly lower than that of pure AP (about 110 ​°C decrease in sample containing 2% by weight of catalyst). Thermal decomposition temperature range of AP was reduced from 178 ​°C to 105 ​°C and 61 ​°C in the samples containing 4% and 2% by weight of catalyst respectively. The results of kinetic calculations obtained from Kissinger method showed effective catalytic performance of this metal-organic framework by increasing the thermal decomposition rate constant of AP more than 1.8 times at a much lower temperature.

Kinetics theoretical study of the O(3P) + C2H6 reaction on an ab initio-based global potential energy surface

Based on a recently developed analytical full-dimensional potential energy surface describing the gas-phase O(3P) + C2H6 reaction (Espinosa-Garcia et al. in Phys Chem Chem Phys 22:22,591, 2020), thermal rate constants and kinetic isotope effects (KIEs) were studied in the temperature range 200–3000 K using three different kinetics tools: variational transition-state theory with multidimensional tunnelling corrections (VTST/MT), ring polymer molecular dynamics (RPMD), and quasi-classical trajectory (QCT) calculations. Except the last method, which failed in the description at low temperatures, as was expected due to its classical nature, the other two methods present rate constants with differences between them of 3% at low temperatures and 25% at high temperatures, simulate the experimental measurements in the intermediate temperature range, 500–1000 K, and are intermediate between two reviews of experimental measurements at low and high temperatures, where the experimental evidence shows differences of a factor of about 5. This result shows that both methods capture quantum effects, such as zero-point energy, tunnelling, and recrossing effects. The kinetics of the title reaction presents a non-Arrhenius behavior, where the activation energy increases with temperature. Two KIEs were analyzed. For the H/D isotopes, the KIE decreases with temperature, from 46.55 to 1.18 in the temperature range 200–3000 K, while the 12C/13C KIE presents values close to unity. Unfortunately, no experimental information is available for comparison.

Effect of Reagent Vibration and Rotation on the State-to-State Dynamics of the Hydrogen Exchange Reaction, H + H2 → H2 + H.

State-to-state dynamics of the benchmark hydrogen exchange reaction H + H2 (v = 0-4, j = 0-3) → H2 (v', j') + H is investigated with the aid of the real wave packet approach of Gray and Balint-Kurti (J. Chem. Phys. 1998, 108, 950-962) and electronic ground BKMP2 potential energy surface of Boothroyd et al. (J. Chem. Phys. 1996, 104, 7139-7152). Initial state-selected and product state-resolved reaction probabilities, integral cross section, and product diatom vibrational and rotational level populations at a few collision energies are reported to elucidate the energy disposal mechanism. State-specific thermal rate constants are also calculated and compared with the available literature results. Coriolis coupling terms of the nuclear Hamiltonian are included, and calculations are parallelized over the helicity quantum number, Ω'. Attempts are made, in particular, to study the effect of reagent vibrational and rotational excitations on the dynamical attributes. It is found that the calculations become computationally expensive with reagent vibrational and rotational excitation. Reagent vibrational excitation is found to enhance the reactivity and has significant impact on the energy disposal to the vibrational and rotational degrees of freedom of the product. The interplay of reagent translational and vibrational energy on the product vibrational distribution unfolds an important aspect of the energy disposal mechanism. The effect of reagent rotation on the state-to-state dynamics is found not to be very significant, and the weak effect turns out to be specific to v'.

Highly efficient extraction of mulberry anthocyanins in deep eutectic solvents: Insights of degradation kinetics and stability evaluation

In this work, an efficient strategy for extracting mulberry anthocyanins using deep eutectic solvents (DESs) was developed. Results show that both the hydrogen bond acceptors and hydrogen bond donors profoundly influenced the density, water content, and viscosity of the DESs. Six newly prepared DESs exhibited higher extraction amounts of anthocyanins than that of the acidified ethanol. Influence factors on choline chloride (ChCl)-lactic acid (HL) (1:2)-mediated extractability were optimized by response surface methodology (RSM). The optimal condition was acquired at 57.24 °C, for 31.54 min, and 10.76 mL/g, where 6.84 ± 0.21 mg/g of anthocyanins was extracted. Notably, the decreased thermal degradation rate constant, improved half-life time, and prolonged storage time of the anthocyanins in ChCl/HL demonstrated the superiority of DESs in the extraction technique over conventional solvents, which might be attributed to the wide and strong hydrogen bond network formed between the DES component with solute and water molecular.

Thermal rate constants for electron attachment to N2O: An example of endothermic attachment.

Rate constants for dissociative electron attachment to N2O yielding O- have been measured as a function of temperature from 400 K to 1000 K. Detailed modeling of kinetics was needed to derive the rate constants at temperatures of 700 K and higher. In the 400 K-600 K range, upper limits are given. The data from 700 K to 1000 K follow the Arrhenius equation behavior described by 2.4 × 10-8 e-0.288 eV/kT cm3 s-1. The activation energy derived from the Arrhenius plot is equal to the endothermicity of the reaction. However, calculations at the CCSD(T)/complete basis set level suggest that the lowest energy crossing between the neutral and anion surfaces lies 0.6 eV above the N2O equilibrium geometry and 0.3 eV above the endothermicity of the dissociative attachment. Kinetic modeling under this assumption is in modest agreement with the experimental data. The data are best explained by attachment occurring below the lowest energy crossing of the neutral and valence anion surfaces via vibrational Feshbach resonances.

Combination Reactions of Propargyl Radical with Hydroxyl Radical and the Isomerization and Dissociation of trans-Propenal.

Ab initio investigation for the ground-electronic potential energy surface (PES) of the CH2CCH + OH combination and the trans-CH2CHCHO isomerization and decomposition has been performed at the UCCSD(T)/CBS(TQ5)//M06-2X/aug-cc-pVTZ level of theory. Thermal and microcanonical rate constants, as well as branching ratios in the 300-2000 K temperature range have been predicted based on optimized structures and vibrational frequencies of species involved using statistical theoretical VRC-TST and RRKM master equation computations. The calculated results are in good agreement with the prior reported data, particularly as an accurate scaling of the energy barriers was carried out. Based on the view of PES and kinetic-predicted values, the reaction paths leading to C2H2 + CO + H2, CH3CH + CO, C2H4 + CO, C2H3 + HCO, and C3H3O + H are the prevailing product channels for the C3H3 + OH bimolecular reaction under the considered 300-2000 K temperature range. Among those products, CH3CH + CO is the most dominant one in the low-temperature condition; however, C2H2 + CO + H2 becomes the most favorable product in the high-temperature region. Alternatively, the C3H4O dissociation processes leading to C2H2 + CO + H2, C2H3 + HCO, C2H4 + CO, and CH2C + CH2O constitute the major paths, in which, C2H2 + CO + H2 is the most critical one with the ∼62% and ∼59% branching ratios at E = 148 and 182 kcal/mol, respectively. The overall second-order rate constants of the bimolecular reaction C3H3 + OH → products obtained at the pressure 760 Torr (Ar) can be illustrated by the modified Arrhenius expression of k(T) = 1.36 × 10-13T1.26 exp[(-1.12 ± 0.43 kcal mol-1)/RT] and/or k(T) = 3.77 × 1017T-7.58 exp[(-18.82 ± 0.20 kcal mol-1)/RT] cm3 molecule-1 s-1, covering the temperature range of 300-1300 and/or 1300-2000 K, respectively. The total high-pressure limit rate constant for the C3H3 + OH → CH2CCHOH barrierless processes is in good agreement with the k(T) = 8.30 × 10-10 T-0.1 cm3 molecule-1 s-1 literature data. Moreover, microcanonical rate constants for the C3H4O isomerization and dissociation are in excellent accordance with the previously predicted values given by Chin and Lee. The present study supplies a thorough insight into the mechanisms and kinetics of the C3H3 + OH combination as well as the C3H4O multistep isomerization/dissociation pathways.

Pilgrim: A thermal rate constant calculator and a chemical kinetics simulator

Pilgrim is a program written in Python and designed to use direct dynamics in the calculation of thermal rate constants of chemical reactions by the variational transition state theory (VTST), based on electronic structure calculations for the potential energy surface. Pilgrim can also simulate reaction mechanisms using kinetic Monte Carlo (KMC).For reaction processes with many elementary steps, the rate constant of each of these steps can be calculated by means of conventional transition state theory (TST) or by using VTST. In the current version, Pilgrim can evaluate thermal rates using the canonical version of reaction-path VTST, which requires the calculation of the minimum energy path (MEP) associated with each elementary step or transition structure. Multi-dimensional quantum effects can be incorporated through the small-curvature tunneling (SCT) approximation. These methodologies are available both for reactions involving a single structure of the reactants and the transition state and also for reactions involving flexible molecules with multiple conformations of the reactant and/or of the transition state. For systems with many conformers, the program can evaluate each of the elementary reaction rate constants by multipath canonical VTST or multi-structural VTST. Moreover, the reactant can be unimolecular or bimolecular.Torsional anharmonicity can be incorporated through either the MSTor or the Q2DTor programs. Dual-level calculations are also available in Pilgrim: automatic high-level single-point energies can be used to correct the energy of reactants, transition states, products, and MEP points using the interpolated single-point energies (ISPE) algorithm.When the rate constants of all the chemical processes of interest are known, by means of their calculation using Pilgrim or alternatively through analytical fits to the rate constants as functions of temperature, it is possible to simulate a multistep mechanism under specified laboratory conditions using KMC. This algorithm allows performing a kinetic simulation to monitor the evolution of each chemical species with time and obtain the product yields. Program summaryProgram Title: PilgrimCPC Library link to program files:http://dx.doi.org/10.17632/24cj4dwxvg.1Developer’s repository link:https://github.com/cathedralpkg/pilgrim/releases; https://comp.chem.umn.edu/pilgrim; https://conservancy.umn.edu/handle/11299/166578Licensing provisions: MITProgramming language: Python 3Nature of problem: Calculation of thermal rate constants for bimolecular and unimolecular chemical reactions and simulation of reaction mechanismsSolution method: The program uses variational transition state theory to calculate thermal rate constants and kinetic Monte Carlo to simulate reaction mechanisms.Restrictions and unusual features: The program cannot treat reactions without saddle points. Unimolecular reactions are calculated only in the high-pressure limit. Direct dynamics calculations with Pilgrim require an electronic structure package to be supplied by the user; currently, Pilgrim supports the Gaussian [Frisch et al. (2003), Frisch et al. (2016a), Frisch et al. (2016b)] and Orca [Neese (2011)] electronic structure packages. Pilgrim has an especially powerful suite of options for handling torsional anharmonicity and multistructural effects.

Preparation and Photochromic Performance of Homogeneous Phase Nitrocellulose Membrane Grafting Spirooxazine Moieties

The synthesis of 1,3,3-trimethyl-9′-acryloxyspiro[indoline-2,3′(3H)naphtho[2,1-b][l,4]-oxazine] (AISO) was carried out by catalytic esterification of 1,3,3-trimethyl-9′-hydroxyspiro-[indoline-2,3′(3H)naphtho[2,1-b][l,4]oxazine] (SO–OH) and acrylic acid in the presence of 1,3-dicyclohexylcarbodiimide (DCC) and N-dimethylaminopyridine (DMAP). Then, the synthesis of the target copolymer (NC-g-AISO) was was carried out by benzoyl peroxide (BPO)-induced graft copolymerization of the AISO monomer onto nitrocellulose (NC) in a homogeneous methyl isobutyl ketone medium. The structure of NC-g-AISO was characterized by Fourier transform infrared (IR) spectroscopy, 13C Nuclear Magnetic Resonance (NMR) spectra and thermogravimetric (TG) analysis. The photochromic properties of NC-g-AISO were investigated by examining UV–Vis spectra in ethyl acetate solution and solid membrane. Compared with the AISO monomer in ethyl acetate solution, the thermal color decay stability of the colored form of NC-g-AISO in ethyl acetate solution and in solid membrane improved significantly. The thermal color decay reaction rate constants in ethyl acetate solution and membrane at 25 °C were 1.77 × 10–2 and 1.36 × 10–3 s–1, respectively, fitted using the first-order reaction equation. After ten photochromic cycles, the relative absorption intensity of the colored form of NC-g-AISO decreased by 0.85%, indicating that the NC-g-AISO membrane has good reversible photochromic behavior.

A Machine Learning Approach for Rate Constants. II. Clustering, Training, and Predictions for the O(3P) + HCl → OH + Cl Reaction.

Following up on our recent paper, which reported a machine learning approach to train on and predict thermal rate constants over a large temperature range, we present new results by using clustering and new Gaussian process regression on each cluster. Each cluster is defined by the magnitude of the correction to the Eckart transmission coefficient. Instead of the usual protocol of training and testing, which is a challenge for present small database of exact rate constants, training is done on the full data set for each cluster. Testing is done by inputing hundreds of random values of the descriptors (within reasonable bounds). The new training strategy is applied to predict the rate constants of the O(3P) + HCl reaction on the 3A' and 3A″ potential energy surfaces. This reaction was recently focused on as a "stress test" for the ring polymer molecular dynamics method. Finally, this reaction is added to the databases and training is done with this addition. The freely available database and new Python software that evaluates the correction to the Eckart transmission coefficient for any reaction are briefly described.

Radiative association of P and Cl atoms

Thermal rate constants for the formation of PCl radical via radiative association have been estimated from potential energy curves and dipole moments calculated by accurate ab initio methods. The formation of PCl through radiative association of $$\hbox {P}(^{4}\hbox {S})$$ and $$\hbox {Cl}(^{2}\hbox {P})$$ atoms occurs mainly through the formation of a quasi-molecule in the A $$^{3}\varPi$$ state, which decays by an allowed dipole transition to the ground $$\hbox {X}^{3}\varSigma ^{-}$$ state. The computed rate constant can be represented over the 300–5000 K temperature range in the form $$k(T)=1.95\times 10^{-20}(T/300)^{0.605}\mathrm{exp}(-1690/T)$$ cm3 s−1 and over the 5000–14,000 K temperature range by the relation $$k(T)=8.53\times 10^{-22}(T/300)^{1.595}\mathrm{exp}(-2.5/T)$$ cm3 s−1, where T is in K.

Surface for methane combustion: O(3P) +CH4 → OH+CH3**Project supported by the National Natural Science Foundation of China (Grant No. 51574016) and completed while the author was in residence at UNSW, Australia supported by the International Cooperation Training Program for Innovative Talents of USTB.

Kinetic investigations including quasi-classical trajectory and canonical unified statistical theory method calculations are carried out on a potential energy surface for the hydrogen-abstraction reaction from methane by atom O(3P). The surface is constructed using a modified Shepard interpolation method. The ab initio calculations are performed at the CCSD(T) level. Taking account of the contribution of inner core electrons to electronic correlation interaction in ab initio electronic structure calculations, modified optimized aug-cc-pCVQZ basis sets are applied to the all-electrons calculations. On this potential energy surface, the triplet oxygen atom attacks methane in a near-collinear H–CH3 direction to form a saddle point with barrier height of 13.55 kcal/mol, which plays a key role in the kinetics of the title reaction. For the temperature range of 298–2500 K, our calculated thermal rate constants for the O(3P) + CH4 → OH + CH3 reaction show good agreement with relevant experimental data. This work provides detailed mechanism of this gas-phase reaction and a theoretical guidance for methane combustion.

The collision cross-sections for proton–argon interaction based on ab initio potential

The classical collision cross-sections of a proton with an argon atom as well as the thermal transport coefficients and rate constant of the colliding $\text{H}^{+}-\text{Ar}$ system are evaluated at the kinetic temperature $T\in [100,10\,000]~(\text{K})$ by means of the asymptotically correct analytical potential constructed for the ground $X^{1}\unicode[STIX]{x1D6F4}^{+}$ state of the ArH+ cation from the highly accurate ab initio data available in the entire range of internuclear distances (Terashkevich et al., J. Quant. Spectrosc. Radiat. Transfer, vol. 234, 2019, pp. 139–146). The results can be useful to estimate thermodynamic, transport and kinetic properties of the Ar/H2 plasma in a wide temperature range.

Influence of pH, temperature, and light on the stability of melatonin in aqueous solutions and fruit juices

The ability to predict melatonin stability during food processing or storage is important. Therefore, the degradation of melatonin in both aqueous solutions and fruit juice samples was investigated. The pH values of aqueous solutions were set over a pH range from 1 to 13 and at four different temperatures (60, 70, 80 and 90 °C). The highest remaining melatonin (CR) was observed in the lowest pH solution (pH = 1, CR > 65%). Melatonin concentrations decreased with rising pH levels from pH 4 to 13 during storage time. The thermal degradation rate constant of melatonin (k) values obtained followed the order: k90°C (0.175) >k80°C (0.123) >k70°C (0.082) >k60°C (0.027). Thermal degradation kinetics followed the first-order reaction model with a high range of coefficients of determination (0.9744 < R2 < 0.995). The temperature also affected on melatonin degradation in fruit juices which the degradation rate was increased with the presence of light and high temperature. Our results can be used as guidelines to develop a processing method that predicts melatonin degradation during thermal processing of food products.

Theoretical Study of the State-resolved Thermal Rate Constants for the Astrophysical Reaction Li + HD+ (v = 0, 1)

Abstract In the present study, we use the time-dependent wave packet (TDWP) method to calculate the thermal rate constants for the reaction Li + HD+(v = 0, 1) → LiH/LiD + H+/D+ in the temperature range of 200–5000 K on the potential energy surface constructed by Martinazzo et al. Total rate constants for both the v = 0 and v = 1 reactions exhibit simple Arrhenius behavior and are compared with previous isotope reactions. Total rate constants for v = 1 are several times larger than those of v = 0, particularly in the low-temperature region. For the two channels of the reaction, the vibrational excitation of HD+ greatly promotes the formation rate of the products LiH and LiD. For v = 0, the rate constants of LiH and LiD are comparable, while for v = 1, the rate constants of LiH are more than two times larger than those of LiD. The state-resolved rate constants show that the products LiH and LiD molecules can be excited to higher vibrational states and are preferably formed with hotter rotational states when the reactant HD+ is vibrationally excited. Applications of these rate constants in the modeling of the astrophysical sources are discussed.

Microcanonical Rate Constants for Unimolecular Reactions in the Low-Pressure Limit.

Low-pressure-limit microcanonical rate constants, κ0(E,J), describe the rate of activating bath gas collisions in a unimolecular reaction and are calculated here using classical trajectories and quantized thresholds for reaction. The resulting semiclassical rate constants are two-dimensional (in total energy E and total angular momentum J) and are intermediate in complexity between the four-dimensional state-to-state collisional energy and angular momentum transfer rate constant, R(E',J';E,J), and the highly averaged thermal rate constant, k0. Results are presented for CH4 (+M), C2Hx (+M), x = 3-6, and H2O (+M), where κ0(E,J) is shown generally to be a sensitive function of the bath gas, temperature, and initial state of the unimolecular reactant. Strong variations in κ0 with respect to E and J lead to complex trends in relative microcanonical bath gas efficiencies. This underlying complexity may complicate the search for simple explanations for observed trends in relative thermal bath gas efficiencies. A different measure of the microcanonical collision efficiency that describes the energy range of activating collisions is introduced that supports the empirical decomposition of collisional activation into separable translational-to-vibrational and rotational-to-vibrational activation mechanisms. The two mechanisms depend differently on mass, temperature, and the J-dependence of the threshold energy for reaction, with rotational-to-vibrational activation favored for heavier baths and for reactions with rigid transition states. Finally, κ0 is used to test the accuracy of several two-dimensional models for R that were proposed for use in master equation studies.

Non-adiabatic quantum dynamics of the electronic quenching OH(A2Σ+) + Kr.

We present the dynamics of the electronic quenching OH(A2Σ+) + Kr(1S) → OH(X2Π) + Kr(1S), with OH(A2Σ+) in the ground ro-vibrational state. This study relies on a new non-adiabatic quantum theory that uses three diabatic electronic states Σ+, Π', and Π'', coupled by one conical-intersection and nine Renner-Teller matrix elements, all of which are explicitly considered in the equation of the motion. The time-dependent mechanism and initial-state-resolved quenching probabilities, integral cross sections, thermal rate constants, and thermally-averaged cross sections are calculated via the real wavepacket method. The results point out a competition among three non-adiabatic pathways: Σ+ ↔ Π', Σ+ ↔ Π'', and Π' ↔ Π''. In particular, the conical-intersection effects Σ+-Π' are more important than the Renner-Teller couplings Σ+-Π', Σ+-Π'', and Π'-Π''. Therefore, Π' is the preferred product channel. The quenching occurs via an indirect insertion mechanism, opening many collision complexes, and the probabilities thus present many oscillations. Some resonances are still observable in the cross sections, which are in good agreement with previous experimental and quasi-classical findings. We also discuss the validity of more approximate quantum methods.

Wave packet quantum dynamics of &lt;inline-formula&gt;&lt;tex-math id="Z-20200417045027-1"&gt;\begin{document}${\bf{C}}{(^3}{\bf{P}}) + {{\bf{H}}_2}({{\bf{X}}^1} \Sigma _{\bf{g}}^ + ) $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="8-20200132_Z-20200417045027-1.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="8-20200132_Z-20200417045027-1.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; &lt;inline-formula&gt;&lt;tex-math id="Z-20200418100246-1"&gt;\begin{document}$ \to {\bf{H}}{(^2}{\bf{S}}) + {\bf{CH}}{(^2} \Pi ) $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="8-20200132_Z-20200418100246-1.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="8-20200132_Z-20200418100246-1.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; reaction based on new CH&lt;sub&gt;2&lt;/sub&gt;(&lt;inline-formula&gt;&lt;tex-math id="M2"&gt;\begin{document}${\tilde {\bf X}{}^3}\bf A''$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="8-20200132_M2.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="8-20200132_M2.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;) surface

The C(&lt;sup&gt;3&lt;/sup&gt;P) + H&lt;sub&gt;2 &lt;/sub&gt;→ CH+H reaction in a collision energy range of 1.0–2.0 eV with the initial state &lt;inline-formula&gt;&lt;tex-math id="M6"&gt;\begin{document}$\nu = 0{\rm{ }},j = 0$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="8-20200132_M6.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="8-20200132_M6.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; is investigated based on the new potential energy surface (PES) by using the Chebyshev wave packet method. All partial wave contributions up to &lt;i&gt;J&lt;/i&gt; = 60 are calculated explicitly by the coupled state (CS) approximation method and the Coriolis coupling (CC) effect. Dynamic properties such as reaction probabilities, integral cross sections, and state specific rate constants are calculated. The calculated probabilities and integral reaction cross sections display an increasing trend with the increase of the collision energy and an oscillatory structure due to the CH&lt;sub&gt;2&lt;/sub&gt; well on the reaction path. The thermal rate constants of the endoergic reaction with a temperature ranging from 1000 K to 2000 K are obtained also. The calculated rate constants increase in the entire temperature range, showing a sharp &lt;i&gt;T&lt;/i&gt; dependence in a range of 1400–2000 K. The rate constants are sensitive to the temperature due to the high threshold of the title reaction. In addition, the results of the exact calculations including CC effect are compared with those from the CS approximation. For smaller &lt;i&gt;J&lt;/i&gt;, the CS probabilities are larger than the CC results, while for larger &lt;i&gt;J&lt;/i&gt;, they are smaller than the CC ones. For reaction cross sections and rate constants, the CS results and the CC ones are in good agreement with each other at lower energy. However, they turn different at higher energy. The comparison between the CC and CS results indicates that neglecting the Coriolis coupling leads the cross sections and the rate constants to be underestimated due to the formation of a CH&lt;sub&gt;2&lt;/sub&gt; complex supported by stationary point of CH&lt;sub&gt;2&lt;/sub&gt;(&lt;inline-formula&gt;&lt;tex-math id="M7"&gt;\begin{document}${\tilde{\rm X}}{}^3 \rm A''$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="8-20200132_M7.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="8-20200132_M7.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;) PES. It is suggested that the CH&lt;sub&gt;2&lt;/sub&gt; complex plays an important role in the process of the title reaction. However, it seems to overestimate the CS and CC rate constants because the barrier recrossing is neglected. Unfortunately, the results obtained in the present work have no corresponding theoretical or experimental data to be compared with, therefore these results provide simply a certain reference significance to the follow-up study of the title reaction.

Rate coefficients and product branching ratios for (E)-2-butenal + H reactions.

Thermal rate constants for the hydrogen abstraction reactions of (E)-2-butenal by hydrogen atoms were calculated, for the first time, using the multipath canonical variational theory with small-curvature tunneling (MP-CVT/SCT). After a torsional potential energy surface exploration, ten conformations of the transition states (including the mirror images) were found and separated into four conformational reaction channels (CRCs). Individual energy paths of each CRC were built, recrossing and quantum tunneling effects estimated, and the thermal rate constants obtained. Due to the hindered rotors, the torsional anharmonicity was incorporated in the rate coefficient through the calculations of the rovibrational partition functions using the extended two-dimensional torsional method (E2DT). For comparison, the one-well (1W-CVT/SCT) and harmonic multipath (MP-CVT/SCT) thermal rate constants were also estimated. In addition, kinetic Monte Carlo (KMC) simulations were performed to predict the product branching ratios. For all kinetic approaches, the formation of products of (R1) is predominant. Compared to the harmonic multipath estimation, the percentage of reaction (R4) increases by approximately 9% when the torsional anharmonicity is taken into account. For the reactions (R2) and (R3), the product branching ratio is slightly decreased when compared with the harmonic simulation.