Product Branching Ratios Research Articles

Theoretical investigation on degradation of CH[triple bond, length as m-dash]CCH2OH by NO3 radicals in the atmosphere.

A detailed computational investigation is executed on the reaction between NO3 and CH[triple bond, length as m-dash]CCH2OH at the CCSD(T)/cc-pVTZ//B3LYP/6-311++G(d,p) level. Addition/elimination and H-abstraction mechanisms are found for the NO3 + CH[triple bond, length as m-dash]CCH2OH reaction, and they could compete with each other. The most feasible addition/elimination pathway through a series of central-C addition, 1,4-H migration to generate intermediates IM1 (CHCONO2CH2OH) and IM3 (CH2CONO2CH2O), and then IM3 directly decompose into product P2 (CH2CONO2CHO + H). The dominant H-abstraction pathway is abstracting the H atom of the -CH2- group to generate h-P1 (CHCCHOH + HNO3). RRKM-TST theory was used to compute the kinetics and product branching ratios of the NO3 + CH[triple bond, length as m-dash]CCH2OH reaction at 200-3000 K. The rate constants at 298 K are consistent with the experimental values. The lifetime of CH[triple bond, length as m-dash]CCH2OH is estimated to be 59.72 days at 298 K. The implicit solvent model was used to examine the solvent effect on the total reaction. Based on the quantitative structure-activity relationship (QSAR) model, the toxicity during the degradation process is increased towards fish, and decreased towards daphnia and green algae.

Mode-Specific Dynamics Studies for the Multichannel C2H2 + OH Reaction.

The C2H2 + OH reaction is a key elementary reaction in acetylene oxidation, and the products forming in different reaction channels, such as C2H and CH3 radicals, are also important for subsequent reaction processes in the combustion process. In this work, we investigated the dynamics of the C2H2 + OH reaction with specific vibrational mode excitations and analyzed the mode specificity based on quasi-classical trajectory calculations on a recently developed full-dimensional potential energy surface. It is found that exciting OH stretching mode can promote the production of H + OCCH2 and CO + CH3, while the excitation of C-H symmetric/antisymmetric stretching mode of C2H2 can facilitate the H2O + C2H channel. Based on the prediction of vibrationally adiabatic and sudden vector projection models, the mode specificity in the C2H2 + OH reaction can be attributed to the difference in the degree of coupling between the initial motion mode and the reaction coordinate of each reaction path, which ultimately leads to the changes in rate constants and the product branching ratios. These findings can offer theoretical insights to regulate the branching ratio of the multichannel C2H2 + OH reaction.

Cu Based Dilute Alloys for Tuning the C2+ Selectivity of Electrochemical CO2 Reduction.

Electrochemical CO2 reduction is a promising technology for replacing fossil fuel feedstocks in the chemical industry but further improvements in catalyst selectivity need to be made. So far, only copper-based catalysts have shown efficient conversion of CO2 into the desired multi-carbon (C2+) products. This work explores Cu-based dilute alloys to systematically tune the energy landscape of CO2 electrolysis toward C2+ products. Selection of the dilute alloy components is guided by grand canonical density functional theory simulations using the calculated binding energies of the reaction intermediates CO*, CHO*, and OCCO* dimer as descriptors for the selectivity toward C2+ products. A physical vapor deposition catalyst testing platform is employed to isolate the effect of alloy composition on the C2+/C1 product branching ratio without interference from catalyst morphology or catalyst integration. Six dilute alloy catalysts are prepared and tested with respect to their C2+/C1 product ratio using different electrolyzer environments including selected tests in a 100-cm2 electrolyzer. Consistent with theory, CuAl, CuB, CuGa and especially CuSc show increased selectivity toward C2+ products by making CO dimerization energetically more favorable on the dominant Cu facets, demonstrating the power of using the dilute alloy approach to tune the selectivity of CO2 electrolysis.

Kinetics and mechanism of the gas-phase reaction of the hydroxyl radical with meta-aminotoluene compound.

An ab initio investigation into the potential energy landscape of the meta-aminotoluene + •OHreaction has been conducted in this study. The calculated results reveal that the reaction channel leading to the product (NHC6H4CH3 + H2O) prevails under the 300-1700K temperature range, while the reaction path forming the product (NH2C6H4CH2 + H2O) dominates in the higher-temperature region (T ≥ 1800K). Within the specified temperature range, the product branching ratio for the former declines from 48 to 30%, while the latter shows an increase, reaching 29%. The overall second-order rate constants of the titled reaction obtained at the pressure 760Torr (N2) can be illustrated by the modified Arrhenius expression of ktotal = 1.46 × 10-13 T0.58 exp[(-0.759kcal.mol-1)/RT] cm3 molecule-1s-1 and ktotal = 1.86 × 10-22 T3.24 exp[(-5.086kcal.mol-1)/RT] cm3 molecule-1s-1, covering the temperature range of T = 300-600K and T > 600K, respectively. The total rate constant at the ambient conditions in this work, 1.43 × 10-11 cm3 molecule-1s-1, has been found to be roughly one order of magnitude lower than the available experimental data, ~ 1.2 × 10-10 cm3 molecule-1s-1, measured by Atkinson et al., Rinke et al., and Witte et al., or the theoretical value, 4.4 × 10-10 cm3 molecule-1s-1, and calculated by Abdel-Rahman and co-workers for the aniline + •OH reaction. The structures of reactants, transition states, intermediate states, and products of the meta-aminotoluene + •OHreaction are calculated with the aug-cc-pVTZ basis set and the methods DFT/B3LYP and CCSD(T). The rate constants and branching ratios in the 300-2000K temperature range are calculated with the statistical theoretical TST and RRKM master equation computations including tunneling corrections, with potential energy surface constructed by the CCSD(T)//B3LYP/aug-cc-pVTZ approach.

Production of singly charm pentaquarks from meson-baryon interactions in B -meson decay

In the paper, we discuss the possible interpretation of the JP=1/2− singly charm pentaquark as hadronic molecules. With the effective Lagrangian method, we further analyze the production properties of singly charm pentaquark from decays of B meson, including strong coupling constants and production branching ratios of the charm pentaquark. Our numerical results show that the branching ratio of production of pentaquark from B meson can reach to order of 10−6. Published by the American Physical Society 2024

Bond-selective effect for the dissociative chemisorption of HOD on the Ni(100) surface revealed at the full-dimensional quantum dynamical level.

We present a comprehensive investigation into the dissociative chemisorption of HOD on a rigid Ni(100) surface using an approximate full-dimensional (9D) quantum dynamics approach, which was based on the time-dependent wave-packet calculations on a full-dimensional potential energy surface obtained through neural network fitting to density functional theory energy points. The approximate-9D probabilities were computed by averaging the seven-dimensional (7D) site-specific dissociation probabilities across six impact sites with appropriate relative weights. Our results uncover a distinctive bond-selective effect, demonstrating that the vibrational excitation of a specific bond substantially enhances the cleavage of that excited bond. The product branching ratios are substantially influenced by which bond undergoes excitation, exhibiting a clear preference for the product formed through the cleavage of the excited bond over the alternative product.

Stress-Alteration Enhancement of the Reactivity of Aluminum Nanoparticles in the Catalytic Decomposition of exo-Tetrahydrodicyclopentadiene (JP-10).

High-energy-density aluminum nanoparticles (AlNPs) upon thermal annealing followed by superquenching result in elevated stress levels in the metallic core and reduced surface energy at the core-shell interface. Isomer-selective vacuum ultraviolet-based photoionization mass spectrometry coupled to a high-temperature chemical microreactor reveals that these stress-altered AlNPs (SA-AlNPs) exhibit distinctive temperature-dependent reactivities toward catalytic decomposition of the hydrocarbon jet fuel exo-tetrahydrodicyclopentadiene (JP-10, C10H16) compared to untreated AlNPs (UN-AlNPs). SA-AlNPs show a delayed initiation of the decomposition for JP-10 by 200 K relative to the UN-AlNPs; however, the full decomposition is achieved at a 100 K lower temperature. Furthermore, there are fewer oxygenated products that are generated from the alumina surface-induced heterogeneous oxidation process and a larger fraction of closed- and open-shell hydrocarbons. Chemical insight bridging the reactivity order of SA-AlNPs at low and high temperatures, simultaneously, is obtained via a detailed examination of the product branching ratios obtained in this study.

Unraveling the Rich Fragmentation Dynamics Associated with S-H Bond Fission Following Photoexcitation of H2S at Wavelengths ∼129.1 nm.

H2S is being detected in the atmospheres of ever more interstellar bodies, and photolysis is an important mechanism by which it is processed. Here, we report H Rydberg atom time-of-flight measurements following the excitation of H2S molecules to selected rotational (JKaKc') levels of the 1B1 Rydberg state associated with the strong absorption feature at wavelengths of λ ∼ 129.1 nm. Analysis of the total kinetic energy release spectra derived from these data reveals that all levels predissociate to yield H atoms in conjunction with both SH(A) and SH(X) partners and that the primary SH(A)/SH(X) product branching ratio increases steeply with ⟨Jb2⟩, the square of the rotational angular momentum about the b-inertial axis in the excited state. These products arise via competing homogeneous (vibronic) and heterogeneous (Coriolis-induced) predissociation pathways that involve coupling to dissociative potential energy surfaces (PES(s)) of, respectively, 1A″ and 1A' symmetries. The present data also show H + SH(A) product formation when exciting the JKaKc' = 000 and 111 levels, for which ⟨Jb2⟩ = 0 and Coriolis coupling to the 1A' PES(s) is symmetry forbidden, implying the operation of another, hitherto unrecognized, route to forming H + SH(A) products following excitation of H2S at energies above ∼9 eV. These data can be expected to stimulate future ab initio molecular dynamic studies that test, refine, and define the currently inferred predissociation pathways available to photoexcited H2S molecules.

Ozonolysis of 2-Methyl-2-pentenal: New Insights from Master Equation Modeling.

Experimental and theoretical studies were carried out to investigate the ozonolysis of trans-2-methyl-2-pentenal. The experiments were conducted in atmospheric simulation chambers coupled to a Fourier transform infrared (FTIR) spectrometer and a gas chromatograph-mass spectrometer at room temperature and atmospheric pressure in the presence of an excess of cyclohexane in dry conditions (RH < 1%). The ozonolysis reaction was investigated theoretically from the results of accurate density functional (M06-2X) and ab initio [CCSD(T)] computations, employing the AVTZ basis set. The sequence of reaction steps was established, and the system of kinetics equations was modeled using MESMER. In the first step, a primary ozonide is formed, which then decomposes along two pathways. The principal ozonolysis products are propanal, methylglyoxal, ethylformate, and a secondary ozonide. An interesting competition between sequential reaction steps and well-skipping is found, which leads to an inversion of the expected methylglyoxal/propanal product ratio at temperatures below 210 K. The mechanism of the "hot ester" reaction channel of the Criegee intermediate was revisited. The computed ozonolysis rate constant and product branching ratio are in excellent agreement with the experimental data that are also reported in the present work.

Predicting pressure-dependent rate constants for the furan + OH reactions and their impact under tropospheric conditions.

In this work, we have evaluated the influence of temperature and pressure on the mechanism of furan oxidation by the OH radical. The stationary points on the potential energy surface were described at the M06-2X/aug-cc-pVTZ level of theory. In the kinetic treatment at the high-pressure limit (HPL), we have combined the multistructural canonical variational theory with multidimensional small-curvature tunneling corrections and long-range transition state theory. The system-specific quantum Rice-Ramsperger-Kassel theory was employed to estimate the pressure-dependent rate. In the HPL, the OH addition on the α carbon is the dominant pathway in the mechanism, producing a product via the ring-opening process, also confirmed by the product branching ratio calculations. The overall rate constant, obtained by a kinetic Monte Carlo simulation, reads the form koverall=5.22×10-13T/3001.10⁡exp1247(K/T) and indicates that the furan oxidation by OH radicals is a pressure-independent reaction under tropospheric conditions.

Measurement of the production branching ratios following nuclear muon capture for palladium isotopes using the in-beam activation method

Measurement of the production branching ratios following nuclear muon capture for palladium isotopes using the in-beam activation method

Combined experimental and computational study of the reactivity of the methanimine radical cation (H2CNH˙+) and its isomer aminomethylene (HCNH2˙+) with propene (CH3CHCH2).

The gas phase reactivity of the radical cation isomers H2CNH˙+ (methanimine) and HCNH2˙+ (aminomethylene) with propene (CH3CHCH2) has been investigated by measuring absolute reactive cross sections and product branching ratios, under single collision conditions, as a function of collision energy (in the range ∼0.07-11.80 eV) using guided ion beam mass spectrometry coupled with VUV photoionization for selective isomer generation. Experimental results have been merged with theoretical calculations to elucidate reaction pathways and structures of products. The H2CNH˙+ isomer is over a factor two more reactive than HCNH2˙+. A major channel from both isomers is production of protonated methanimine CH2NH2+via hydrogen-atom transfer reaction but, while H2CNH˙+ additionally gives charge and proton transfer products, the HCNH2˙+ isomer leads instead to protonated vinylimine CH2CHCHNH2+, produced alongside CH3˙ radicals. The reactions have astrochemical implications in the build up of chemical complexity in both the interstellar medium and the hydrocarbon-rich atmospheres of planets and satellites.

Pressure and temperature dependent kinetics and the reaction mechanism of Criegee intermediates with vinyl alcohol: a theoretical study.

Criegee intermediates (CIs), the key intermediates in the ozonolysis of olefins in atmosphere, have received much attention due to their high activity. The reaction mechanism of the most simple Criegee intermediate CH2OO with vinyl alcohol (VA) was investigated by using the HL//M06-2X/def2TZVP method. The temperature and pressure dependent rate constant and product branching ratio were calculated using the master equation method. For CH2OO + syn-VA, 1,4-insertion is the main reaction channel while for the CH2OO + anti-VA, cycloaddition and 1,2-insertion into the O-H bond are more favorable than the 1,4-insertion reaction. The 1,4-insertion or cycloaddition intermediates are stabilized collisionally at 300 K and 760 torr, and the dissociation products involving OH are formed at higher temperature and lower pressure. The rate constants of the CH2OO reaction with syn-VA and anti-VA both show negative temperature effects, and they are 2.95 × 10-11 and 2.07 × 10-13 cm3 molecule-1 s-1 at 300 K, respectively, and the former is agreement with the prediction in the literature.

Isomeric and rotational effects in the chemi-ionisation of 1,2-dibromoethene with metastable neon atoms.

The specific geometry of a molecule can have a pronounced influence on its chemical reactivity. However, experimental data on reactions of individual molecular isomers are still sparse because they are often difficult to separate and frequently interconvert into one another under ambient conditions. Here, we employ a novel crossed-beam experiment featuring an electrostatically controlled molecular beam combined with a source for radicals and metastables to spatially separate the cis and trans stereoisomers as well as individual rotational states of 1,2-dibromoethene and study their specific reactivities in the chemi-ionisation reaction with excited neon atoms. The experiments reveal pronounced isomeric and rotational specificities in the rates and product branching ratios of the reaction. The present study underlines the importance and combined role of molecular geometry and of rotational motion in the dynamics of chemi-ionisation reactions.

High-accuracy DMBE potential energy surface for CNO(A''4) and the rate coefficients for the C + NO reaction in the A'2, A''2, and A''4 states.

An accurate potential energy surface (PES) for the lowest lying A''4 state of the CNO system is presented based on explicitly correlated multi-reference configuration interaction calculations with quadruple zeta basis set (MRCI-F12/cc-pVQZ-F12). The abinitio energies are fitted using the double many-body expansion method, thus incorporating long-range energy terms that can accurately describe the electrostatic and dispersion interactions with physically motivated decaying functions. Together with the previously fitted lowest A'2 and A''2 states using the same theoretical framework, this constitutes a new set of PESs that are suitable to predict rate coefficients for all atom-diatom reactions of the CNO system. We use this set of PESs to calculate thermal rate coefficients for the C(P3) + NO(Π2) reaction and compare the temperature dependence and product branching ratios with experimental results. The comparison between theory and experiment is shown to be improved over previous theoretical studies. We highlight the importance of the long-range interactions for low-temperature rate coefficients.

Atmospheric Photo-Oxidation of 2-Ethoxyethanol: Autoxidation Chemistry of Glycol Ethers.

We investigate the gas-phase photo-oxidation of 2-ethoxyethanol (2-EE) initiated by the OH radical with a focus on its autoxidation pathways. Gas-phase autoxidation─intramolecular H-shifts followed by O2 addition─has recently been recognized as a major atmospheric chemical pathway that leads to the formation of highly oxygenated organic molecules (HOMs), which are important precursors for secondary organic aerosols (SOAs). Here, we examine the gas-phase oxidation pathways of 2-EE, a model compound for glycol ethers, an important class of volatile organic compounds (VOCs) used in volatile chemical products (VCPs). Both experimental and computational techniques are applied to analyze the photochemistry of the compound. We identify oxidation products from both bimolecular and autoxidation reactions from chamber experiments at varied HO2 levels and provide estimations of rate coefficients and product branching ratios for key reaction pathways. The H-shift processes of 2-EE peroxy radicals (RO2) are found to be sufficiently fast to compete with bimolecular reactions under modest NO/HO2 conditions. More than 30% of the produced RO2 are expected to undergo at least one H-shift for conditions typical of modern summer urban atmosphere, where RO2 bimolecular lifetime is becoming >10 s, which implies the potential for glycol ether oxidation to produce considerable amounts of HOMs at reduced NOx levels and elevated temperature. Understanding the gas-phase autoxidation of glycol ethers can help fill the knowledge gap in the formation of SOA derived from oxygenated VOCs emitted from VCP sources.

Hydration Rearrangement in the 4-Aminobenzonitrile-(H2 O)2 Cluster Induced by Photoionization: The Effect of Solvent-Solvent Interactions.

The interplay between solute-solvent and solvent-solvent interactions plays an essential role in solvation dynamics that has important effects on the mechanism and dynamics of chemical reactions in solution. In this study, the rearrangement of the hydration shell induced by photoionization of a solute molecule is probed in a state- and isomer-specific manner by resonant multiphoton ionization detected IR spectroscopy of the prototypical 4-aminobenzonitrile-(H2 O)2 cluster produced in a molecular beam. IR spectra reveal that the water molecules form a cyclic solvent network around the CN group in the initial neutral state (S0 ). Different from the singly-hydrated cluster, in which either the CN or the NH2 group is hydrated, hydration of the NH2 group is not observed in the dihydrated cluster. IR spectra obtained after ionizing the solute molecule into the cation ground state (D0 ) exhibit features ascribed to both NH-bound and CN-bound isomers, indicating that water molecules migrate from the CN to the NH site upon ionization with a yield depending on the ionization excess energy. Analysis of the IR spectra as a function of the excess energy shows that migration produces two different NH2 solvated structures, namely (i) the most stable structure in which both N-H bonds are singly hydrated and (ii) the second most stable isomer in which one of the N-H bonds is hydrated by a H-bonded (H2 O)2 dimer. The product branching ratio of the two isomers depends on the excess energy. The role of the water-water interaction in the hydration rearrangement is discussed based on the potential energy landscape. Solvation dynamics plays an important role in reaction mechanisms in the condensed phase, where not only solute-solvent solvation but also solvent-solvent interactions have a significant influence on the dynamics. Thus, the investigation of solvation dynamics at the molecular level substantially contributes to our understanding of the reaction mechanism. In this study, the dihydrated cluster of 4ABN was utilized as a model for the first solvation layer to elucidate solvent motions induced by ionization of the solute and the role of W-W interactions for the solvent relaxation.

Measurements of rate coefficients of CN+, HCN+, and HNC+ collisions with H2 at cryogenic temperatures.

The experimental determination of the reaction rate coefficients for production and destruction of HCN+ and HNC+ in collision with H2 is presented. A variable-temperature, 22-pole radio frequency ion trap was used to study the reactions in the temperature range 17-250K. The obtained rate coefficients for the reaction of CN+ and HCN+ with H2 are close to the collisional (Langevin) value, whereas that for the reaction of HNC+ with H2 is quickly decreasing with increasing temperature. The product branching ratios for the reaction of CN+ with H2 are also reported and show a notable decrease of the HNC+ product with respect to the HCN+ product with increasing temperature. These measurements have consequences for current astrochemical models of cyanide chemistry, in particular, for the HCNH+ cation.

Theoretical study on the reactions of n-CnH2n+1OH (n = 1–4) with C2H5 radicals: Predicted rate constants and branching ratios

The mechanisms of the reactions of n-CnH2n+1OH (n = 1–4) with C2H5 radical have been investigated by both CCSD(T) and B3LYP methods. Our results show that the reactions can occur via H-abstraction channels with energy barriers of 11.9–16.7 kcal/mol. The rate constants and product branching ratios have been calculated for the temperature range of 300–2500 K. The results show that all of the products via H abstraction channels can contribute at high temperatures (>2000 K). The optimized geometries of the related species and predicted heats of reactions agree well with available data.

Constructing Diabatic Potential Energy Matrices with Neural Networks Based on Adiabatic Energies and Physical Considerations: Toward Quantum Dynamic Accuracy.

A permutation invariant polynomial-neural network (PIP-NN) approach for constructing the global diabatic potential energy matrices (PEMs) of the coupled states of molecules is proposed. Specifically, the diabatization scheme is based merely on the adiabatic energy data of the system, which is ideally a most convenient way due to not requiring additional ab initio calculations for the data of the derivative coupling or any other physical properties of the molecule. Considering the permutation and coupling characteristics of the system, particularly in the presence of conical intersections, some vital treatments for the off-diagonal terms in diabatic PEM are essentially needed. Taking the photodissociation of H2O()/NH3() and nonadiabatic reaction Na(3p) + H2 → NaH(Σ+) + H for example, this PIP-NN method is shown to build up the global diabatic PEMs effectively and accurately. The root-mean-square errors of the adiabatic potential energies in the fitting for three different systems are all small (<10 meV). Further quantum dynamic calculations show that the absorption spectra and product branching ratios in both H2O() and NH3() nonadiabatic photodissociation are well reproduced on the new diabatic PEMs, and the nonadiabatic reaction probability of Na(3p) + H2 → NaH(Σ+) + H obtained on the new diabatic PEMs of the 12A1 and 12B2 states is in reasonably good agreement with previous theoretical result as well, validating this new PIP-NN method.