Two versions of the double-layered composite methods, including the restricted open-shell model chemistry based on the complete basis set quadratic mode (DL-ROCBS-Q) and the extrapolated CBS limit of electronic energy on the basis of the coupled cluster with single, double, and noniterative triple excitations with the hierarchical sequence of the correlation-consistent basis sets (DL-RCCSD(T)/CBS), were developed to calculate the energetic reaction routes for the systems involving 13/14 heavy atoms with good balance between efficiency and accuracy. Both models have been employed to investigate the oxidation reactions of heptafluoroisobutyronitrile ((CF3)2CFCN) with hydroxyl radical. The (CF3)2CFCN + OH reaction is dominated by the C–O addition/elimination routes as bifurcated into trans- and cis-conformations. Although the formation of isocyanic acid or hydrogen fluoride is highly exothermic, the major nascent product was predicted to be the less exoergic cyanic acid. Preference of the product channels could be tuned by the single water molecule in the presence of the H2O–HO complex. The production of amide compound was found to be the most significant route accompanied by the OH regeneration. Moreover, the OH radical could be an efficient catalyst for the hydrolysis of (CF3)2CFCN. Implication of the current theoretical results in the chemistry of (CF3)2CFCN for both atmospheric sink and potential dielectric replacement gas was discussed.

Electronic structures of [(trifluoromethyl)imino]sulfur difluoride (CF3NSF2) and degradation mechanisms by hydroxyl radical have been investigated using density functional theory (M06-2X), the complete basis set quadratic CBS-Q, and the explicitly correlated coupled-cluster methods [CCSD(T)-F12]. The d-function augmented correlation-consistent basis sets including triple- and quadruple-ξ were employed for the sulfur-containing species. It was found that CF3NSF2 exists as two conformations connected by the internal rotation of CF3 around the central NS bond. The distorted syn conformer is more stable than the symmetrical anti conformer. The nitrogen–sulfur link in CF3NSF2 was revealed to be predominantly ionic CF3N––+SF2 in structure rather than the conventional N═S double bond on the basis of natural bond orbital analysis. OH radical prefers to attach on the S atom of CF3NSF2 along the opposite direction of the S—F bond via a nucleophilic addition mechanism with a barrier of 2.9 kcal/mol whereas the ON association pathway is negligible. Although many product channels are thermodynamically favorable, none of them is kinetically accessible because of the significant barriers along the reaction routes. However, the degradation of CF3NSF2 by OH can be accelerated considerably in the presence of a single water molecule, which acts as a bridge for the consecutive proton migration within the floppy cyclic geometries. The half-life of CF3NSF2 was estimated to be 2.5 year, and the final products are exclusively CF3NH and SF2O. Theoretical calculation supports that CF3NSF2 is an environment-friendly green gas. It is worthy of testing its dielectric properties to replace SF6 for practical use.

Covalent organic frameworks (COFs) represent an emerging class of porous crystalline materials and have recently shown interesting applications in energy storage. Herein, we report the construction of a cycle-stable sulfur electrode by embedding sulfur into a 2D COF. The designed porphyrin-based COF (Por-COF), featuring a relatively large pore volume and narrow pore size distribution, has been employed as a host material for sulfur storage in Li–S batteries. With a 55% sulfur loading in the composite, the thus-prepared cathode delivers a capacity of 633 mA h g−1 after 200 cycles at 0.5C charge/discharge rates. Therefore, embedding sulfur in the nanopores of the Por-COF significantly improves the performance of the sulfur cathode. Considering the flexible design of COFs, we believe that it is possible to synthesize a 2D COF host with a suitable pore environment to produce more stable Li–S batteries, which may help in exploration of the structure–property relationship between the host material and cell performance.

•Detailed mechanisms for the O+CF3I reaction are revealed.•Singlet-triplet surface crossing dominates the association of O with CF3I.•The IO production involves stepwise mechanism.•The singlet CF3IO should be detectable.•Rate constants for the O+CF3I reaction are pressure-independent.Both singlet and bifurcated triplet (3A″ and 3A′) potential energy surfaces for the O+CF3I reaction were explored systematically using density functional M06-2X method with the triple- and quadruple-ζ quality and small-core energy-consistent relativistic pseudopotentials. Single-point energies were calculated using the explicitly correlated CCSD(T)-F12 method. On the triplet surface, the association of O(3P) with CF3I leads to the weakly bound complexes. The subsequent decomposition or isomerization surmounts high barriers, indicative of the little importance of the triplet energetic routes for the title reaction. On the singlet surface, a deep well corresponding to the s-CF3IO intermediate exists. Moreover, the singlet-triplet surface crossing to form s-CF3IO from the O(3P)+CF3I has been characterized by locating the minimum on the seam of intersection using the multireference SA-CASSCF method and the single-point energy computations with RS2 and MRCISD methods. It was identified that the subsequent CI bond decomposition of singlet s-CF3IO is the dominant mechanism for the IO radical production in the O(3P)+CF3I reaction. Neither atomic iodine nor IF molecule production is significant because of the high barrier for the isomerization of s-CF3IO to s-CF3OI. The energies of some key stationary points on the dominant reaction routes were corrected with CCSDT, CCSDT(Q), and an extrapolation to FCI, together with spin-orbit coupling and diagonal Born-Oppenheimer correction. The theoretical rate constants are in good agreement with the available experimental data. The overall rate constants exhibit positive temperature dependence in the range 200–3000 K and could be expressed as k(T) = 6.6 × 10−12 (T/298)0.74 e−108/T cm3 molecule−1 s−1. No pressure dependence of the rate constant has been found.Singlet-Triplet crossing mechanisms for the O+CF3I reaction.

The direct reaction kinetic method of low pressure fast discharge flow (DF) with resonance fluorescence monitoring of OH (RF) has been applied to determine rate coefficients for the overall reactions OH + C2H5F (EtF) (1) and OH + CH3C(O)F (AcF) (2). Acetyl fluoride reacts slowly with the hydroxyl radical, the rate coefficient at laboratory temperature is k2(300 K) = (0.74 ± 0.05) × 10–14 cm3 molecule–1 s–1 (given with 2σ statistical uncertainty). The temperature dependence of the reaction does not obey the Arrhenius law and it is described well by the two-exponential rate expression of k2(300–410 K) = 3.60 × 10–3 exp(−10500/T) + 1.56 × 10–13 exp(−910/T) cm3 molecule–1 s–1. The rate coefficient of k1 = (1.90 ± 0.19) × 10–13 cm3 molecule–1 s–1 has been determined for the EtF-reaction at room temperature (T = 298 K). Microscopic mechanisms for the OH + CH3C(O)F reaction have also been studied theoretically using the ab initio CBS-QB3 and G4 methods. Variational transition state theory was employed to obtain rate coefficients for the OH + CH3C(O)F reaction as a function of temperature on the basis of the ab initio data. The calculated rate coefficients are in good agreement with the experimental data. It is revealed that the reaction takes place predominantly via the indirect H-abstraction mechanism involving H-bonded prereactive complexes and forming the nascent products of H2O and the CH2CFO radical. The non-Arrhenius behavior of the rate coefficient at temperatures below 500 K is ascribed to the significant tunneling effect of the in-the-plane H-abstraction dynamic bottleneck. The production of FC(O)OH + CH3 via the addition/elimination mechanism is hardly competitive due to the significant barriers along the reaction routes. Photochemical experiments of AcF were performed at 248 nm by using exciplex lasers. The total photodissociation quantum yield for CH3C(O)F has been found significantly less than unity; among the primary photochemical processes, C–C bond cleavage is by far dominating compared with CO-elimination. The absorption spectrum of AcF has also been determined by displaying a strong blue shift compared with the spectra of aliphatic carbonyls. Consequences of the results on atmospheric chemistry have been discussed.

The reactions of hydroperoxy radicals with hydroxymethylperoxy and methoxymethylperoxy radicals were studied using the hybrid density functional theory and the coupled-cluster theory with complete basis set extrapolation. In contrast with the unsubstituted alkylperoxy reactions, it was found that OH-substitution has a significant effect on the reaction mechanism. Several hydrogen bonding reaction precursors exist at the start of the reaction. The reaction pathways show a strongly anisotropic character. The preferred transition states are four-, five-, six-, or seven-membered cyclic structures. The predicted rate coefficients are expressed as k(T) = 8.48 × 10−24T3.55e2164/T + 2.37 × 10−29T4.70e3954/T cm3 molecule−1 s−1. Based on the available experimental data in the temperature range 275–333 K, the theoretical and experimental results are in agreement with a relative average deviation of only 8%. The nascent products at low and high temperatures are hydroperoxide molecules and hydroxyl radicals, respectively. A potential source has been found for the production of formic acid and new insights into the experimental observations are presented.

Formic acid was used as the model of lauric acid to investigate the microscopic mechanism of the anti-icing behavior and was checked to find out if it can be catalyzed to produce H2 for fuel cells by the α-Al2O3(0001) 2 × 2 supercell slab model. The density functional theory with the all-electron double numerical polarized basis sets was employed. The results show that when it involves the carboxyl O and hydroxyl H atom the 1,2-dissociated adsorbate is the most stable intermediate on the dry Al2O3(0001) surface and is energetic barrier free to form the fairly stable ROCO- and HO-covered surface with the binding energy of 59.5 kcal/mol, and this dissociation mode has the lowest energy barrier of 14.9 kcal/mol to form the HOCO- and H2O-covered surface after the surface is fully hydroxylated. The energetic barrier of the HCOOH dehydrogenation and dehydration reactions on the alumina surface decreased considerably from 65.3 to 30.6 kcal/mol and from 62.1 to 26.8 kcal/mol, respectively, in comparison with the gaseous decomposition. The dissociated configuration of lauric acid was tested, and it was found that it dissociated with free energy barrier through 1,2-hydrogen migration into the C11H23OCO- and HO-covered surface with a binding energy of 60.7 kcal/mol. The present theoretical work is useful to gain some new insights on the microscopic interaction mechanism of the superhydrophobic alumina surface fabrication procedure and on the heterogeneous catalysis reactions of the H2 production.

The anionic mechanisms for the elementary dimerization reaction of monosilicic acid in basic aqueous solution have been characterized comprehensively using various ab initio methods. Many new insights into the silicate oligomerization reaction, which is fundamentally important in sol–gel chemistry, zeolite synthesis, and cement hydration, are presented in this work. Conformational dependence of the dimerization reaction is proposed in view of hundreds of conformations with various inter- and intramolecular hydrogen bonding patterns along the reaction routes. An alternative water cleavage route from the five-coordinated silicon intermediate is revealed. The detour involves a six-center cyclic transition state, which is more preferable energetically than the well-known four-center water removal step. By including explicit water molecules, the activation barrier of the four-center water cleavage path can be reduced considerably to be even lower than the first barrier of the Si–O bond formation. In contrast, the six-center detour is less affected by the additional water molecules due to the unfavorable geometric distortion. The new understanding of the dimerization mechanism could have considerable impact on the initial stages of silica nucleation.

•The rate determining step of SF4 hydrolysis is the SN2 substitution reaction.•The hydrolyzing reaction heats in aqueous solution are larger than in gas phase.•Self-catalysis remarkably reduces the activation energy of SF4 hydrolysis.•Intermediates prefer dehydrofluorination rather than further hydrolysis.•SOF2 and FSOOH are the important intermediates from SF4 to SO2.The reaction between sulfur tetrafluorine (SF4) and H2O was computationally investigated using the G4//MP2/6-311G(d, p) theoretical model. Among four reactive channels in the initial attack process, the primary path, which occurred via a SN2 displacement reaction to produce SF3OH, is the rate-determining step in the complete hydrolysis of SF4, resulting in the formation of SO2 (H2SO3). The energy barrier (i.e., 22.48 kcal mol−1) in the gas phase will be substantially reduced when catalyzed by H2O and/or HF, and the Berry pseudorotation reaction (BPR) process of SF3OH becomes the rate-controlling step. The hydrolysis mechanism of SF4 in aqueous solution and the activation energy of the rate-determining step using the PCM model do not substantially change compared to the gas phase results. The hydrolysis of SF4 in an aqueous solution has a higher enthalpy. For secondary reactions in aqueous solution, the intermediates are prone to dehydrofluorination instead of hydrolysis. Although the activation energy of SOF2 hydrolysis is higher than that of SF4, the relative energy of the former is lower than that of the latter in aqueous solution. Therefore, SOF2 might be an important intermediate for the formation of SO2.Among four reactive channels in the initial attacking of water on sulfur atom of SF4, three of them are SN2 substitution reactions while the other one is combination reaction. The rate-determining step of the hydrolysis of SF4 has a barrier height of 22.48 kcal mol−1 to generate intermediate SF3OH. SOF2 may be further formed through the dehydrofluorination of SF3OH.

•Improvement of B3LYP.•Parameterization optimization.•Organic reaction mechanism.•Enthalpy of formation.The B3LYP hybrid density functional has been used for decades but its three empirical parameters were copied straightforwardly from the B3PW91 functional. We found that the serious flaw of B3LYP for the enthalpies of formation of large organic molecules and the qualitative failure of B3LYP for organic chemical reactivity are caused by these arbitrary parameters. Using the rigorously optimized empirical parameters, namely, a0 = 0.20, ax = 0.67, and ac = 0.84, B3LYP does outperform the old formula significantly with the comparable or even better performance than the state-of-the-art density functionals. It is suggested that the B3LYP method with the optimized semiempirical parameters might continue to be a good density functional in chemistry especially in the calculations of thermochemistry and reactivity of large organic molecules.Graphical abstractThe general quantitative failure of B3LYP for the enthalpies of formation of large alkane molecules and the qualitative flaw of B3LYP for the organic Smiles reaction results from the arbitrary empirical parameters. With the rigorously optimized parameters, the performance of B3LYP becomes as good as the latest functionals and the high-level ab initio methods.

TIP4P/2005 force-field-based classical molecular dynamics simulations were employed to investigate the microscopic mechanism for the ice growth from supercooled water when the external electric (0–109 V/m) and magnetic fields (0–10 T) are applied simultaneously. Using the direct coexistence ice/water interface, the anisotropic effect of electric and magnetic fields on the basal, primary prismatic, and the secondary prismatic planes of ice Ih has been calculated. It was revealed for the first time that the solvation shells of supercooled water could be affected by the cooperative electric and magnetic fields. Meanwhile, the self-diffusion coefficient is lowered, and the shear viscosity increases considerably. The critical electric and magnetic fields to accelerate ice growth on the prismatic plane are fairly low (ca. 106 V/m and 0.01 T). In contrast, the basal plane is hardly affected unless the fields increase to the order 109 V/m and 10 T. Rotational dynamics of water molecules might play an important role in ice growth with the applied external fields. Density functional theory with the triple numerical all-electron basis set was used to reveal the electronic structures of the basal and primary prismatic planes of ice Ih with respect to the anisotropic effect of ice growth.

The mechanism and kinetics of the reaction of acrylonitrile (CH2CHCN) with hydroxyl (OH) has been investigated theoretically. This reaction is revealed to be one of the most significant loss processes of acrylonitrile. BHandHLYP and M05-2X methods are employed to obtain initial geometries. The reaction mechanism conforms that OH addition to CC double bond or C atom of –CN group to form the chemically activated adducts, 1-IM1(HOCH2CHCN), 2-IM1(CH2HOCHCN), and 3-IM1(CH2CHCOHN) via low barriers, and direct hydrogen abstraction paths may also occur. Temperature- and pressure-dependent rate constants have been evaluated using the Rice–Ramsperger–Kassel–Marcus theory. The calculated rate constants are in good agreement with the experimental data. At atmospheric pressure with N2 as bath gas, 1-IM1(OHCH2CHCN) formed by collisional stabilization is the major product in the temperature range of 200–1200 K. The production of CH2CCN and CHCHCNviahydrogen abstractions becomes dominant at high temperatures (1200–3000 K).

The microscopic reaction mechanism for the water adsorption/dissociation processes on the α-Al2O3(0001) surface was calculated using density functional theory with the all-electron triple numerical polarized basis sets. Both unit-cell and 2 × 2 supercell slab models were employed to investigate the coverage-dependent hydroxylation of the surface. Geometries of the molecular adsorbed intermediates, transition states, and the hydroxylated products were fully optimized, and the energetic reaction routes were clarified. The hydroxylation occurs predominantly via the low-barrier 1,4-hydrogen migration path, and the 1,2-dissociation path is competitive. The 1,2-hydroxylated surface is more preferable thermodynamically in the consideration of reaction exothermicity. It was found that the in-plane hydrogen atoms can roam between the surface oxygen atoms, resulting in isomerization between the 1,2- and 1,4-hydroxylated products. Calculations for the multiple layer adsorption confirm that the hydroxylated surface is relatively inert to further hydroxylation by water. Further added water molecules prefer to form multilayered hexagonal ice-like arrangements through a hydrogen-bonding network. The electric field might not play a significant role in either surface reconstruction or the hydroxylation process until it exceeds 108 V/m. The present theoretical work is useful to gain some new insights on the ice accumulation of high-voltage power lines under high humidity and supercooled environment.

The mechanism of the reaction of imidogen (NH) with fulminic acid (HCNO) has been investigated theoretically using the multiconfigurational self-consistent-field theory (MCSCF), multireference Rayleigh−Schrodinger perturbation theory (RSPT2), and coupled cluster theory (CC) along with the complete basis set extrapolations (CBS). The calculations show that the NH + HCNO reaction takes place via an N → C addition mechanism predominantly by surmounting a small barrier (ca. ∼3 kcal/mol). The adduct is HC(NH)NO in the triplet state with an exothermicity of more than 60 kcal/mol. The subsequent C−N cleavage, which is nearly barrierless, leads to HCNH and NO as the final products. This represents the most energetically favorable product channel of the title reaction. The channels leading to HCN, HNC, HNO, or HON via O- or H-migration mechanisms involve higher barriers and thus are negligible. The singlet−triplet crossing has been investigated as well for the HCNH + NO product channel by locating the conical interactions. Using transition state theory, the rate constants were predicted as a function of temperatures. It is suggested that the NH + HCNO reaction might be an alternative source for the NO regeneration under the combustion conditions. This calculation is useful to simulate experimental investigations of the NH + HCNO reaction.

Ab intitio molecular dynamics simulation of the electronic structure of the aqueous superoxide anion (O2−) has been carried out using the Car−Parrinello density functional theory at 298 and 310 K. The modeling system consists of one O2− solvated in 31 water molecules. On the basis of our 40 ps production run, the novel mechanism and the nature of the hydration of the superoxide anion in a relatively big aqueous environment have been revealed by using various radial distribution functions. The averaged coordinated water number was estimated to be 4.5. The calculated microscopic configurations of the first solvation shell are in good agreement with the experimental results. The vibrational frequency of the solvated O2− anion was red-shifted significantly in comparison with that of the free radical anion in the gas phase. The diffusion coefficient of O2− was estimated to be about 8 × 10−5 cm2/s at 298 K. Comparisons with the previous force-field-based classical molecular dynamics simulations have been made, and the differences were discussed.

The reaction of triplet methylene with methanol is a key process in alcohol combustion but surprisingly this reaction has never been studied. The reaction mechanism is investigated by using various high-level ab initio methods, including the complete basis set extrapolation (CBS-QB3 and CBS-APNO), the latest Gaussian-n composite method (G4), and the Weizmann-1 method (W1U). A total of five product channels and six transition states are found. The dominant mechanism is direct hydrogen abstraction, and the major product channel is CH3 + CH3O, involving a weak prereactive complex and a 7.4 kcal/mol barrier. The other hydrogen abstraction channel, CH3 + CH2OH, is less important even though it is more exothermic and involves a similar barrier height. The rate coefficients are predicted in the temperature range 200−3000 K. The tunneling effect and the hindered internal rotational freedoms play a key role in the reaction. Moreover, the reaction shows significant kinetic isotope effect.

Mechanisms and kinetics of the NCCO + O2 reaction have been investigated using the extrapolated full coupled cluster theory with the complete basis set limit (FCC/CBS) and multichannel RRKM theory. Energetically, the most favorable reaction route involves the barrierless addition of the oxygen atom to one of the carbon atoms of NCCO and the subsequent isomerization−decomposition via the four-center intermediate and transition state, leading to the final products NCO and CO2. At 298 K, the calculated overall rate constant is strongly pressure-dependent, which is in good agreement with the available experimental values. It is predicted that the high-pressure limit rate constants exhibit negative temperature dependence below 350 K. The dominant products are NCO and CO2 at low pressures (ca. <10 Torr) and the NCCO(O2) radical at higher pressures, respectively.

Covalent organic frameworks (COFs) represent an emerging class of porous crystalline materials and have recently shown interesting applications in energy storage. Herein, we report the construction of a cycle-stable sulfur electrode by embedding sulfur into a 2D COF. The designed porphyrin-based COF (Por-COF), featuring a relatively large pore volume and narrow pore size distribution, has been employed as a host material for sulfur storage in Li–S batteries. With a 55% sulfur loading in the composite, the thus-prepared cathode delivers a capacity of 633 mA h g−1 after 200 cycles at 0.5C charge/discharge rates. Therefore, embedding sulfur in the nanopores of the Por-COF significantly improves the performance of the sulfur cathode. Considering the flexible design of COFs, we believe that it is possible to synthesize a 2D COF host with a suitable pore environment to produce more stable Li–S batteries, which may help in exploration of the structure–property relationship between the host material and cell performance.

The mechanism and kinetics of the reaction of acrylonitrile (CH2CHCN) with hydroxyl (OH) has been investigated theoretically. This reaction is revealed to be one of the most significant loss processes of acrylonitrile. BHandHLYP and M05-2X methods are employed to obtain initial geometries. The reaction mechanism conforms that OH addition to CC double bond or C atom of –CN group to form the chemically activated adducts, 1-IM1(HOCH2CHCN), 2-IM1(CH2HOCHCN), and 3-IM1(CH2CHCOHN) via low barriers, and direct hydrogen abstraction paths may also occur. Temperature- and pressure-dependent rate constants have been evaluated using the Rice–Ramsperger–Kassel–Marcus theory. The calculated rate constants are in good agreement with the experimental data. At atmospheric pressure with N2 as bath gas, 1-IM1(OHCH2CHCN) formed by collisional stabilization is the major product in the temperature range of 200–1200 K. The production of CH2CCN and CHCHCNviahydrogen abstractions becomes dominant at high temperatures (1200–3000 K).

The anionic mechanisms for the elementary dimerization reaction of monosilicic acid in basic aqueous solution have been characterized comprehensively using various ab initio methods. Many new insights into the silicate oligomerization reaction, which is fundamentally important in sol–gel chemistry, zeolite synthesis, and cement hydration, are presented in this work. Conformational dependence of the dimerization reaction is proposed in view of hundreds of conformations with various inter- and intramolecular hydrogen bonding patterns along the reaction routes. An alternative water cleavage route from the five-coordinated silicon intermediate is revealed. The detour involves a six-center cyclic transition state, which is more preferable energetically than the well-known four-center water removal step. By including explicit water molecules, the activation barrier of the four-center water cleavage path can be reduced considerably to be even lower than the first barrier of the Si–O bond formation. In contrast, the six-center detour is less affected by the additional water molecules due to the unfavorable geometric distortion. The new understanding of the dimerization mechanism could have considerable impact on the initial stages of silica nucleation.

The reactions of hydroperoxy radicals with hydroxymethylperoxy and methoxymethylperoxy radicals were studied using the hybrid density functional theory and the coupled-cluster theory with complete basis set extrapolation. In contrast with the unsubstituted alkylperoxy reactions, it was found that OH-substitution has a significant effect on the reaction mechanism. Several hydrogen bonding reaction precursors exist at the start of the reaction. The reaction pathways show a strongly anisotropic character. The preferred transition states are four-, five-, six-, or seven-membered cyclic structures. The predicted rate coefficients are expressed as k(T) = 8.48 × 10−24T3.55e2164/T + 2.37 × 10−29T4.70e3954/T cm3 molecule−1 s−1. Based on the available experimental data in the temperature range 275–333 K, the theoretical and experimental results are in agreement with a relative average deviation of only 8%. The nascent products at low and high temperatures are hydroperoxide molecules and hydroxyl radicals, respectively. A potential source has been found for the production of formic acid and new insights into the experimental observations are presented.