Reaction of CH3O2 and HO2: Ab initio characterization of dimer structure and vibrational mode analysis for reaction mechanisms

All species involved in the multi‐channel reaction of CH₃O₂ with HO₂ have been investigated using density functional theory (DFT). The molecular geometries for various species are optimized employing the B3LYP method implementing the 6‐311++G** basis set. The relative energies of all species are calculated at the same level theory. The results show that there are two kinds of channels: singlet and triplet. The singlet channel involves four intermediates and six transition states. The triplet channel includes two intermediates and two transition states. There are four kinds of reaction products: CH₃OOH + ¹O₂, CH₃OH + O₃, CH₄ + 2O₂, and CH₃OOH + ³O₂. The vibrational mode analysis is used to elucidate the relationships of the intermediates, the transition states, and the products. The extensive investigation shows that the reaction mechanism is reliable. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

A two‐step reaction scheme leading to singlet carbene species that can be detected under matrix conditions for the reaction of Zr(3F) with either CH3F or CH3CN

The results obtained from CASSCF‐MRMP2 calculations are used to rationalize the singlet complexes detected under matrix‐isolation conditions for the reactions of laser‐ablated Zr(³F) atoms with the CH₃F and CH₃CN molecules, without invoking intersystem crossings between electronic states with different multiplicities. The reaction Zr(³F) + CH₃F evolves to the radical products ZrF· + ·CH₃. This radical asymptote is degenerate to that emerging from the singlet channel of the reactants Zr(¹D) + CH₃F because they both exhibit the same electronic configuration in the metal fragment. Hence, the caged radicals obtained under cryogenic‐matrix conditions can recombine through triplet and singlet paths. The recombination of the radical species along the low‐multiplicity channel produces the inserted structures H₃C? Zr? F and H₂C?ZrHF experimentally detected. For the Zr(³F) + CH₃CN reaction, a similar two‐step reaction scheme involving the radical fragments ZrNC· + ·CH₃ explains the presence of the singlet complexes H₃C? Zr? NC and H₂C?Zr(H)NC revealed in the IR‐matrix spectra upon UV irradiation. © 2014 Wiley Periodicals, Inc.     

Theoretical investigation of ion pair SN2 reactions of alkali isothiocyanates with alkyl halides. Part 1. Reaction of lithium isothiocyanate and methyl fluoride with inversion mechanism

The gas‐phase ionic S_N2 reactions NCS^‐ + CH₃F and ion pair S_N2 reaction LiNCS + CH₃F with inversion mechanism were investigated at the level of MP2(full)/6‐311+G**//HF/6‐311+G**. Both of them involve the reactants complex, inversion transition state, and products complex. There are two possible reaction pathways in the ionic S_N2 reaction but four reaction pathways in the ion pair S_N2 reaction. Our results indicate that the introduction of lithium significantly lower the reaction barrier and make the ion pair displacement reaction more facile. For both ionic and ion pair reaction, methyl thiocyanate is predicted to be the major product, but the latter is more selective. More‐stable methyl isothiocyanate can be prepared by thermal rearrangement of methyl thiocyanate. The theoretical predictions are consistent with the known experimental results. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Mechanism and rate constants of the CH2 + CH2CO reactions in triplet and singlet states: A theoretical study

Ab initio and density functional CCSD(T)-F12/cc-pVQZ-f12//B2PLYPD3/6-311G** calculations have been performed to unravel the reaction mechanism of triplet and singlet methylene CH₂ with ketene CH₂CO. The computed potential energy diagrams and molecular properties have been then utilized in Rice–Ramsperger–Kassel–Marcus-Master Equation (RRKM-ME) calculations of the reaction rate constants and product branching ratios combined with the use of nonadiabatic transition state theory for spin-forbidden triplet-singlet isomerization. The results indicate that the most important channels of the reaction of ketene with triplet methylene lead to the formation of the HCCO + CH₃ and C₂H₄ + CO products, where the former channel is preferable at higher temperatures from 1000 K and above. In the C₂H₄ + CO product pair, the ethylene molecule can be formed either adiabatically in the triplet electronic state or via triplet-singlet intersystem crossing in the singlet electronic state occurring in the vicinity of the CH₂COCH₂ intermediate or along the pathway of CO elimination from the initial CH₂CH₂CO complex. The predominant products of the reaction of ketene with singlet methylene have been shown to be C₂H₄ + CO. The formation of these products mostly proceeds via a well-skipping mechanism but at high pressures may to some extent involve collisional stabilization of the CH₃CHCO and cyclic CH₂COCH₂ intermediates followed by their thermal unimolecular decomposition. The calculated rate constants at different pressures from 0.01 to 100 atm have been fitted by the modified Arrhenius expressions in the temperature range of 300–3000 K, which are proposed for kinetic modeling of ketene reactions in combustion. © 2018 Wiley Periodicals, Inc.     

Reaction of propionitrile with methylidyne: A theoretical study

The results of a CCSD(T)-F12/cc-pVTZ-f12//ωB97XD/cc-pVTZ quantum-chemical study of the potential energy surface (PES) for the reaction of propionitrile with methylidyne are combined with Rice-Ramsperger-Kassel-Marcus (RRKM) calculations of the reaction rate constants and product branching ratios in the deep space conditions corresponding to the zero-pressure limit at various collision energies. The most energetically favorable reaction pathways have been identified. The reaction outcome has been shown to strongly depend on the branching in the entrance reaction channel, between CH additions and insertions into various C-H and C-C bonds. For instance, CH addition to the N atom predominantly leads to 3H-pyrrole + H (p9), with CH₂NC + C₂H₄ (p2) also being a significant product. CH addition to the triple C≡N bond mostly results in 2-methylene-2H-azirine + CH₃ (p13), whereas CH insertions into C-H bonds in the CH₃ and CH₂ groups of propionitrile form CH₂CN + C₂H₄ (p1) and CH₂CHCN + CH₃ (p7) respectively. Less likely CH insertions into single C-C bonds yield CH₃CHCHCN + H (p5) and CH₂CHCH₂CN + H (p8). The results indicate that the methylidyne + propionitrile reaction may represent a critical step toward the formation of heterocyclic N-containing molecules in the interstellar medium and in planetary atmospheres.     

Reaction of photogenerated fluorine atoms with dopant molecules in solid argon

The products of reactions of dopant CH₄ molecules with F atoms diffusing in solid argon at 20–30 K were identified by ESR and FTIR spectroscopy. The F atoms stabilized in the matrix were generated by UV photolysis of Ar?CH₄(CD₄)?F (1000∶1∶1) samples at 13 K. Subsequent heating above 20 K results in thawing off diffusion of the F atoms and formation of products of their reaction with CH₄: radical-molecular complexes^·CH₃?HF (^·CD₃?DF) and radicals^·CH₃ (^·CD₃). The ESR spectra of the radicala are similar to those observed for matrix-isolated^·CH₃. The^·CH₃?HF complexes are characterized by the IR band of HF stetching vibration at 3764 cm^?1. Two additional splittings on the H (a _H·=2 G) and F(a _F=16G) nuclei of the HF molecule appeal in the ESR spectrum of the complex. The latter splitting is retained in the^·CD₃?DF complex, whereA _D· <0.3G The rate constant of the reaction CH₄+F→^·CH₃+HF is equal to ?10^?25 cm³s^?1 at 20 K. Its activation energy (1.7±0.2 kcal mol^?1) is ?0.5 kcal mol^?1 greater than that in the gas phase. The collinear C_3v-configuration of the^·CH₃?HF complex, which is similar to the configuration of the reagents in the transition state of the reaction considered, was established by the comparison of the exprrimental constants of hyperfine coupling with the results of the quantum-chemical calculation.     

The DFT study on mechanisms for NCO with C2H5 reaction

A detailed investigation has been performed at the QCISD(T)/6‐311++G(d,p)//B3LYP/6‐311+G(d,p) level for the reaction of NCO with C₂H₅ by constructing singlet and triplet potential energy surfaces (PES). The results show that the title reaction is more favorable on the singlet PES than on the triplet PES. On the singlet PES, the initial addition processes are barrierless and release lots of energy. The dominant channel occurs via the fragmentations of the initial adduct C₂H₅NCO and C₂H₅OCN to form C₂H₄ + HNCO and HOCN, respectively. With higher barrier heights, other products such as CH₄ + HNC + CO, CH₃CHNH + CO, CH₃CH + HNCO, and CH₃CN + H₂ + CO are less competitive. On the triplet PES, the entrance reactions surpass significant barriers; therefore, it could be negligible at the normal atmospheric condition. However, the most feasible channel on the triplet PES is the direct hydrogen abstraction channel to form CH₂CH₂ + HNCO. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Reaction of CH3CHO with Y+: A density functional theoretical study

The reaction mechanism of the Y⁺ cation with CH₃CHO has been investigated with a DFT approach. All the stationary points are determined at the UB3LYP/ECP/6-311++G** level of the theory. Both ground and excited state potential energy surfaces are investigated in detail. The present results show that the title reaction start with the formation of a CH₃CHO-metal complex followed by C-C, aldehyde C-H, methyl C-H and C-O activation. These reactions can lead to four different products (Y⁺CH₄ + CO, Y⁺CO + CH₄, Y⁺COCH₂ + H₂ and Y⁺O + C₂H₄). The minimum energy reaction path is found to involve the spin inversion in the different reaction steps, this potential energy curve-crossing dramatically affects reaction exothermic. The present results may be helpful in understanding the mechanism of the title reaction and further experimental investigation of the reaction.     

Mechanism and Rate Constants of the CH3+ CH2CO Reaction: A Theoretical Study

The mechanism of the reaction of ketene with methyl radical has been studied by ab initio CCSD(T)‐F12/cc‐pVQZ‐f12//B2PLYPD3/6‐311G** calculations of the potential energy surface. Temperature‐ and pressure‐dependent reaction rate constants have been computed using the Rice–Ramsperger–Kassel–Marcus (RRKM)–Master Equation and transition state theory methods. Three main channels have been shown to dominate the reaction; the formation of the collisionally stabilized CH₃COCH₂ radical and the production of the C₂H₅ + CO and HCCO + CH₄ bimolecular products. Relative contributions of the CH₃COCH₂, C₂H₅ + CO, and HCCO + CH₄ channels strongly depend on the reaction conditions; the formation of thermalized CH₃COCH₂ is favored at low temperatures and high pressures, HCCO + CH₄ is dominant at high temperatures, whereas the yield of C₂H₅ + CO peaks at intermediate temperatures around 1000 K. The C₂H₅ + CO channel is favored by a decrease in pressure but remains the second most important reaction pathway after HCCO + CH₄ under typical flame conditions. The calculated rate constants at different pressures are proposed for kinetic modeling of ketene reactions in combustion in the form of modified Arrhenius expressions. Only rate constant to form CH₃COCH₂ depends on pressure, whereas those to produce C₂H₅ + CO and HCCO + CH₄ appeared to be pressure independent.     

Cis‐1‐phosphabicyclo[3.3.0]octan

A new approach to 1‐phosphabicyclo[3.3.0]octane compounds starts from the reaction of 4‐chloro‐hepta‐1.6‐diene with Mg in THF. No Grignard rearrangement is observed. The Grignard reagent is converted into 1‐allyl‐3‐butenylphosphonous dichloride followed by reduction with LiAlH₄. Cis‐1‐phosphabicyclo[3.3.0]octane has been prepared by radical‐initiated cyclization of 1‐allyl‐3‐butenylphosphane. The bicyclic phosphane is characterized by analytical data as well as ³¹P and ¹³C NMR measurements and the reactionswith NO, S₈, KSeCN, CH₃I, Ni(CO)₄ and HSO₃F, respectively.     

A density functional theory study on the atmospheric reaction of CH3O2 with HS: Mechanism and kinetics

The reaction mechanism of CH₃O₂ and HS was systematically investigated by density functional theory (DFT). Six singlet pathways and seven triplet ones are located on the potential surface (PES). The result indicates that the main products are CH₃O and HSO both on the singlet and triplet PES, different from the CH₃O₂ + OH reaction. Moreover, deformation density (ρ_def) and atoms in molecules (AIM) analyses were carried out to further uncover the nature of chemical bonding evolution in the primary pathways. Furthermore, reaction rate constants were calculated in the temperature range from 200 to 1000 K using the transition state theory with the Wigner and Eckart tunneling corrections. Our results can shed light on the title reaction and offer instructions for analogous atmospheric reactions, as well as experimental research in the future.     

Reaction Mechanism Investigation Using Vibrational Mode Anal—ysis for the Multichannel Reacition of CH3O＋CO

On the basis of the computed results got by the Gaussian 94 package at B3LYP/6-311 G** level,the reaction mechanism of CH3O radical with CO has been investiagted thoroughly via the vibrational model analysis ,And the relationships among the reactants,eight transition states,four intermediates and various products involved this multichannel reation are eluci-dated,The vibrational mode anaysis shows that the reaction mechanism is relialbe.     

Theoretical Study on the Reaction Mechanism of Ketene CH2CO with Isocyanate NCO Radical

The bimolecular single collision reaction potential energy surface of an isocyanate NCO radical with a ketene CH2CO molecule was investigated by means of B3LYP and QCISD（T） methods. The computed results indicate that two possible reaction channels exist on the surface. One is an addition-elimination reaction process, in which the CH2CO molecule is attacked by the nitrogen atom at its methylene carbon atom to lead to the formation of the intermediate OCNCH2CO followed by a C-C rupture channel to the products CH2NCO＋CO. The other is a direct hydrogen abstraction channel from CHzCO by the NCO radical to afford the products HCCO＋HNCO. Because of a higher barrier in the hydrogen abstraction reaction than in the addition-elimination reaction, the direct hydrogen abstraction pathway can only be considered as a secondary reaction channel in the reaction kinetics of NCO＋ CH2CO. The predicted results are in good agreement with previous experimental and theoretical investigations.     

Theoretical study on the atmospheric reaction of CH3O2 with OH

A quantum chemical investigation on the reaction mechanism of CH₃O₂ with OH has been performed. Based on B3LYP and QCISD(T) calculations, seven possible singlet pathways and seven possible triplet pathways have been found. On the singlet potential energy surface (PES), the most favorable channel starts with a barrierless addition of O atom to CH₃O₂ leading to CH₃OOOH and then the O? O bond dissociates to give out CH₃O + HO₂. On the triplet PES, the calculations indicate that the dominant products should be ³CH₂O₂ + H₂O with an energy barrier of 29.95 kJ/mol. The results obtained in this work enrich the theoretical information of the title reaction and provide guidance for analogous atmospheric chemistry reactions. © 2015 Wiley Periodicals, Inc.     

The visible chemiluminescence of the reaction F + CH3F

By using molecular beam apparatus the visible (450–900 nm) chemiluminescence of the reaction F + CH₃F was investigated. Seven vibronic bands of HCF (Ã₁A-XA') and four vibrational bands of HF ground state overtone transitions were obtained. The relative vibrational state distributions of HF (V'=4,5,6) states and the rotational temperature of HF (V'=3) state were obtained. The analyses show that the two kinds of spectra were caused by the secondary reaction F+CH₃F. The results may be helpful to explain the contradictory results of the experiments in F+CH₃F system.     

Assessing the Viability of the Methylsulfinyl Radical-Ozone Reaction

Although integral to remote marine atmospheric sulfur chemistry, the reaction between methylsulfinyl radical (CH₃SO) and ozone poses challenges to theoretical treatments. The lone theoretical study on this reaction reported an unphysically large barrier of 66 kcal mol⁻¹ for abstraction of an oxygen atom from O₃ by CH₃SO. Herein, we demonstrate that this result stems from improper use of MP2 with a single-reference, unrestricted Hartree-Fock (UHF) wavefunction. We characterized the potential energy surface using density functional theory (DFT), as well as multireference methodologies employing a complete active-space self-consistent field (CASSCF) reference. Our DFT PES shows, in contrast to previous work, that the reaction proceeds by forming an addition adduct [CH₃S(O₃)O] in a deep potential well of 37 kcal mol⁻¹. An O−O bond of this adduct dissociates via a flat, low barrier of 1 kcal mol⁻¹ to give CH₃SO₂+O₂. The multireference computations show that the initial addition of CH₃SO+O₃ is barrierless. These results provide a more physically intuitive and accurate picture of this reaction than the previous theoretical study. In addition, our results imply that the CH₃SO₂ formed in this reaction can readily decompose to give SO₂ as a major product, in alignment with the literature on CH₃SO reactions.     

A theoretical study of the photolytic decomposition of ethane ethylene via a triplet-state ethylidene intermediate

The complete geometrically optimized triplet state of ethane, using the MINDO/2 method, spontaneously dissociates into CH₃H; and H₂. The reaction paths for rearrangement of CH₃CH: to CH₂CH₂ in the triplet state is calculated. The activation energy was determined to be 19.4 kcal/mole. These results are discussed in the context of previously reported experimental results for the gas phase photolyses of alkanes.     

A study of the reactions of fluorine with hydrogen and methane in the initiation phase using a miniature tubular reactor

A small tubular reactor having an inner diameter of 1–2 mm andused as the source in a molecular beam apparatus is described in detail. This arrangement allows the study of fast reactions with reaction times smaller than 1 msec. The preexplosive reaction phase between F₂ and H₂ and CH₄, respectively, is investigated to find out the initiation reactions. In the F₂/H₂ reaction, initiation is brought about by heterogeneous generation of F atoms or some other surface reaction. Evidence is also obtained for chain branching reactions. In the F₂/CH₄ case the dominant initiation reaction is the homogeneous reaction CH₄ + F₂ → CH₃ + HF + F. The rate constant for the reaction between 300 and 400 K is 10^12.3±0.3 exp[?47 ± 8 kJ/mol/RT] cm³/mol sec. The analysis of the experimental data also yields the rate constant for the propagation reaction CH₃ + F₂ → CH₃ F + F, which is 10^12.3±0.3 exp[?4.6 ±2.1 kJ/mol/RT] cm³/mol sec.     

Insight into the reaction mechanism of CH2SH with HO2: A density functional theory study

Density functional theory was adopted in this work to reveal the reaction mechanism of CH₂SH with HO₂. Reaction rate constants were computed from 200 to 2000 K using the transition state theory combined with Wigner and Eckart tunneling correction. Moreover, localized orbital locator, atoms in molecules and Mayer bond order analyses were used to study the essence of chemical bonding evolution. Eleven singlet paths and three triplet ones are located on the potential surface (PES). The results show that the main products on the singlet PES are ¹CH₂S and H₂O₂, whereas on the triplet PES they are CH₃SH + ³O₂, which are coincident with the similar reaction of CH₃S and HO₂. This conclusion is also supported by rate constant calculation results. Interestingly, all the possible paths are involved in the hydrogen transfer. The results have provided underlying insights to the analogous reactions and further experimental studies.