Theoretical insights into the gaseous and heterogeneous reactions of halogenated phenols with ˙OH radicals: mechanism, kinetics and role of (TiO2)n clusters in degradation processes.

Halogenated phenols are highly toxic chemicals with serious health risks, and the removal of these persistent environmental pollutants remains a challenge. Based on quantum chemistry calculations, the homogeneous/heterogeneous degradation mechanism and kinetics of C6X5OH (X = F, Cl, and Br) initiated by ˙OH radicals in the gas phase and TiO2 cluster surfaces are investigated in this work. Four ˙OH-addition and one proton-coupled electron-transfer (PCET) reaction channels for each halogenated phenol were found and the ˙OH-addition channels were more favorable than the PCET pathway without TiO2 clusters. At 296 K, the calculated total rate constant for ˙OH with C6F5OH in the atmosphere well agreed with the limited experimental data of (6.88 ± 1.37) × 10-12 cm3 molecule-1 s-1. The lifetimes of C6F5OH, C6Cl5OH, and C6Br5OH were about 12.04-12.86 h at 296 K, which favored their medium-range transport in the atmosphere. In the presence of (TiO2)n clusters (n = 4, 6, 8, 12, and 16), the PCET mechanism for hydrogen transfer reaction of C6F5OH with ˙OH radicals was changed from the previous four-electron/three-center into four-electron/two-center, which results in the PCET pathway becoming more favorable than the ˙OH-addition channels. Meanwhile, the heterogeneous degradation rate constants of C6F5OH were accelerated by more than 10 orders of magnitude within 200-430 K compared with those of the naked reaction. The effects of (TiO2)n cluster (n = 4, 6, 8, 12, and 16) size on the degradation rates were analyzed at 200-430 K, and the reaction on the (TiO2)8 cluster had a faster rate. The subsequent reactions including the bond cleavage of the benzene ring and O2 addition or abstraction were studied. This work provides new insights into halogenated aromatic atmospheric chemistry and nanoscale TiO2 photocatalysis in air or wastewater management.

Metal-free catalysis for the reaction of nitrogen dioxide dimer with phenol: An unexpected favorable source of nitrate and aerosol precursors in vehicle exhaust.

Atmospheric reaction mechanism and dynamics of phenol with nitrogen dioxide dimer were explored by the density functional theory and high-level quantum chemistry combined with statistical kinetic calculations within 220-800 K. The nitric acid and phenyl nitrite, the typical aerosol precursors, are the preponderant products because of the low formation free energy barrier (∼8.7 kcal/mol) and fast rate constants (∼10-15 cm3 molecule-1 s-1 at 298 K). Phenyl nitrate is the minor product and it would be also formed from the transformation of phenyl nitrite in NO2-rich environment. More importantly, kinetic effects and catalytic mechanism of a series of metal-free catalysts (H2O, NH3, CH3NH2, CH3NHCH3, HCOOH, and CH3COOH) on the title reaction were investigated at the same level. The results indicate that CH3NH2 and CH3NHCH3 can not only catalyze the title reaction by lowering the free energy barrier (about 1.4-6.5 kcal/mol) but also facilitate the production of organic ammonium nitrate via acting as a donor-acceptor of hydrogen. Conversely, the other species are non-catalytic upon the title reaction. The stabilization energies and donor-acceptor interactions in alkali-catalyzed product complexes were explored, which can provide new insights to the properties of aerosol precursors. Moreover, the lifetime of phenol determined by nitrogen dioxide dimer in the presence of dimethylamine may compete with that of determined by OH radicals, indicating that nitrogen dioxide dimer is responsible for the elimination of phenol in the polluted atmosphere. This work could help us thoroughly understand the removal of nitrogen oxides and phenol as well as new aerosol precursor aggregation in vehicle exhaust.

Aliovalent-Ion-Induced Lattice Regulation Based on Charge Balance Theory: Advanced Fluorophosphate Cathode for Sodium-Ion Full Batteries.

There are still many problems that hinder the development of sodium-ion batteries (SIBs), including poor rate performance, short-term cycle lifespan, and inferior low-temperature property. Herein, excellent Na-storage performance in fluorophosphate (Na3 V2 (PO4 )2 F3 ) cathode is achieved by lattice regulation based on charge balance theory. Lattice regulation of aliovalent Mn2+ for V3+ increases both electronic conductivity and Na+ -migration kinetics. Because of the maintaining of electrical neutrality in the material, aliovalent Mn2+ -introduced leads to the coexistence of V3+ and V4+ from charge balance theory. It decreases the particle size and improves the structural stability, suppressing the large lattice distortion during cathode reaction processes. These multiple effects enhance the specific capacity (123.8 mAh g-1 ), outstanding high-rate (68% capacity retention at 20 C), ultralong cycle (only 0.018% capacity attenuation per cycle over 1000 cycles at 1 C) and low-temperature (96.5% capacity retention after 400 cycles at -25 °C) performances of Mn2+ -induced Na3 V1.98 Mn0.02 (PO4 )2 F3 when used as cathode in SIBs. Importantly, a feasible sodium-ion full battery is assembled, achieving outstanding rate capability and cycle stability. The strategy of aliovalent ion-induced lattice regulation constructs cathode materials with superior performances, which is available to improve other electrode materials for energy storage systems.

Atmospheric oxidation of fluoroalcohols initiated by ˙OH radicals in the presence of water and mineral dusts: mechanism, kinetics, and risk assessment.

The transport and formation of fluorinated compounds are greatly significant due to their possible environmental risks. In this work, the ˙OH-mediated degradation of CF3CF2CF2CH2OH and CF3CHFCF2CH2OH in the presence of O2/NO/NO2 was studied by using density functional theory and the direct kinetic method. The formation mechanisms of perfluorocarboxylic/hydroperfluorocarboxylic acids (PFCAs/H-PFCAs), which were produced from the reactions of α-hydroxyperoxy radicals with NO/NO2 and the ensuing oxidation of α-hydroxyalkoxy radicals, were clarified and discussed. The roles of water and silica particles in the rate constants and ˙OH reaction mechanism with fluoroalcohols were investigated theoretically. The results showed that water and silica particles do not alter the reaction mechanism but obviously change the kinetic properties. Water could retard fluoroalcohol degradation by decreasing the rate constants by 3-5 orders of magnitude. However, the heterogeneous ˙OH-rate coefficients on the silica particle surfaces, including H4SiO4, H6Si2O7, and H12Si6O18, are larger than that of the naked reaction by 1.20-24.50 times. This finding suggested that these heterogeneous reactions may be responsible for the atmospheric loss of fluoroalcohols and the burden of PFCAs. In addition, fluoroalcohols could be exothermically trapped by H12Si6O18, H6Si2O7, and H4SiO4, in which the chemisorption on H12Si6O18 is stronger than that on H6Si2O7 or H4SiO4. The global warming potentials and radiative forcing of CF3CF2CF2CH2OH/CF3CHFCF2CH2OH were calculated to assess their contributions to the greenhouse effect. The toxicities of individual species were also estimated via the ECOSAR program and experimental measurements. This work enhances the understanding of the environmental formation of PFCAs and the transformation of fluoroalcohols.

Atmospheric chemistry of thiourea: nucleation with urea and roles in NO2 hydrolysis.

Nitrogenous particle participation in the formation of clusters has attracted considerable attention from numerous researchers in recent years. Urea and thiourea (TU), as the common fertilizers in agriculture, have a significant impact on the atmospheric environment, whereas their implications have not been comprehended widely. Herein, we have used quantum calculations and ABCluster to explore the potential roles of thiourea and urea in particle formation events. A vital implication of these results is that they may contribute toward particle formation in marine environments and Asia region where the concentration of thiourea and urea has been increasing for a few years. Furthermore, the mechanisms of NO2 hydrolysis in the presence of thiourea and subsequent reactions were studied deeply. The results indicate that, although these reactions are not thermodynamically favorable at 298.15 K under homogeneous gas-phase conditions, thiourea may promote the hydrolysis of NO2 in heterogeneous environments containing very high concentrations of these molecules. The kinetics analysis shows that the rate constants of the hydrolysis reaction catalyzed by thiourea with N2O4-W and TU-W are about 2-5 and 1-2 orders of magnitude faster than those of the naked reaction. Thiourea nitrate and its aquo-complex were also studied, and the results suggest that the reaction produced an acid-base complex in which the trans- configuration is the final form for nitrous acid. We hope that these findings would inspire field measurements for detecting urea and thiourea in the troposphere.

DFT analysis on the removal of dimethylbenzoquinones in atmosphere and water environments: ·OH-initiated oxidation and captured by (TiO2)n clusters (n=1-6).

The elimination mechanisms and the dynamics of 2,5-dimethylbenzoquinone/2,6-dimethylbenzoquinone are performed by DFT under the presence of ·OH radical and TiO2-clusters. The rate coefficients, calculated within the atmospheric and combustion temperature range of 200-2000 K, agree well with the experimental data. The subsequent reactions including the bond cleavage of quinone ring, O2 addition or abstraction, the reactions of peroxy radical with NO yielding the precursor of organic aerosol are studied. Gaseous water molecule plays an important role in the transformation of alkoxy radical and exhibits a catalytic performance in the enol-ketone tautomerism. The lifetimes of 2,5-dimethylbenzoquinone/2,6-dimethylbenzoquinone are about 12.04-12.86 h at 298 K, which are in favor of the medium range transport of them in the atmosphere. Significantly, the water environment plays a negative role on the ·OH-degradation of dimethylbenzoquinone. Compared to the quinone ring, 2,5-dimethylbenzoquinone onto (TiO2)n clusters (n = 1-6) is easier to be absorbed by TiO2-clusters through its oxygen site because of its strong chemisorption, which indicates that TiO2-clusters are capable of trapping dimethylbenzoquinones effectively. The water environment could weaken the adsorption of 2,5-dimethylbenzoquinone onto (TiO2)n clusters (n = 1-6) by increasing the adsorption energy. This work reveals the removal of dimethylbenzoquinones and the formation of organic aerosol under polluted environments.

Ciprofloxacin transformation in aqueous environments: Mechanism, kinetics, and toxicity assessment during •OH-mediated oxidation.

The initial reactions of organics with •OH are important to understand their transformations and fates in advanced oxidation processes in aqueous phase. Herein, the kinetics and mechanism of •OH-initiated degradation of ciprofloxacin (CIP), an antibiotic of fluoroquinolone class, are obtained using density functional and computational kinetics methods. All feasible mechanisms are considered, including H-abstraction, •OH-addition, and sequential electron proton transfer. Results showed that the H-abstraction is the dominant reaction pathway, and the product radicals P7H, P9H, and P10H are the dominating intermediates. The aqueous phase rate coefficients for the •OH-triggered reaction of ciprofloxacin are calculated from 273 K to 323 K to examine the temperature dependent effect, and the theoretical value of 6.07 × 109 M-1 s-1 at 298 K is close to the corresponding experimental data. Moreover, the intermediates P7H, P9H, and P10H could easily transform to several stable products in the presence of O2, HO2•, and •OH. The peroxy radical, which is generated from the incorporation of H-abstraction product radicals (P7H, P9H, and P10H) with O2, prefers to produce HO2• into the surrounding through direct concerted elimination rather than the indirect mechanism. In addition, the peroxy radical could react with HO2• via triplet and singlet routes, and the former is more favorable due to its smaller barrier compared with the latter. The hydroxyl-substituted CIP has higher activity than its parent compound in their reactions with •OH due to its lower barrier and faster rate. In addition, the -NHC(O)-containing compound IM3-P10-H-4 is harmful to aquatic fish and is the primary product in the •OH-rich environment according to the ecotoxicity assessment computations. This study can improve our comprehension on CIP transformation in complex water environments.

Theoretical study on the mechanisms of the decomposition of nitrate esters and the stabilization of aromatic amines.

The nitrate esters are important components of double-base propellants. Aromatic amines are recommended as the stabilizers to delay the decomposition of nitrate esters and increase their storage time. The decomposition mechanisms of alkyl, alkoxy dinitrate, and poly-fluoride nitrate esters and the stabilizing effect of aromatic amines including new designed phenols are studied at the level of B3LYP/6-31G**. Alkyl and alkoxyl dinitrate esters are likely to be transformed by hydrogen abstraction, which is consistent with that of mononitrate and trinitrate esters. However, for poly-fluoride nitrate esters, NO2 catalyzed self-decomposition is preferred. In addition, comparing with mononitrate and trinitrate esters, the order of their stability is mononitrates > dinitrates > trinitrates. Poly-fluoride nitrate esters have a poorer stability than non-fluorinated nitrate esters. Comparing with parent nitrate esters, the stability of new designed poly-fluoride oxygen-containing nitrate esters is slightly improved. Aromatic amines including new designed phenols are effective stabilizers of nitrate esters, especially when introduced hydroxyl in the para position, can enhance the effects of stabilizers. The rate constants for the decomposition of nitrate esters and the bimolecular reaction between stabilizers and NO2 are calculated by using traditional transition state theory. Graphical abstractComparison between the reaction energy barrier of nitrate esters and stabilizers with NO2.

Theoretical study of H-atom abstraction reactions from CH3CH2OCH2CH3, CHF2CF2OCH2CF3 and CF3CH2OCH3 by NO3 radical & subsequent degradation.

The nocturnal reactions of CH3CH2OCH2CH3, CHF2CF2OCH2CF3 and CF3CH2OCH3 initiated by NO3 radicals are important sources of alkyl radicals and nitric acids. In this paper, the thermodynamics and kinetics of CH3CH2OCH2CH3, CHF2CF2OCH2CF3 and CF3CH2OCH3 induced by NO3 radical in gas phase are studied in detail by BHandHLYP method combined with 6-311G(d,p) basis set, and the single point correction is calculated by relatively accurate CCSD(T) method. In the temperature range of 200-400 K, the rate constants of title reactions are fitted to the three-parameter Arrhenius formula: k1 = 1.13 × 10-40T9.24exp(1675.99/T) k2 = 2.23 × 10-23T2.81exp(-4476.24/T) k3 = 5.63 × 1043T-19.20exp(-9344.12/T) All the rate constants calculated by the canonical variational transition state theory and the small curvature tunneling are basically consistent with the limited experimental data. By comparing the reaction rate constants of ethyl ether and its isomer methyl propyl ether with NO3 radical at 293 ±â€¯2 K, the higher the symmetry is, the faster the reaction rate of ether is. Thermodynamic calculations and kinetic data of the title reactions indicate that the H-abstraction reactions at the -OCH2- sites are the main reaction pathways. The thermodynamic and kinetic data of the reaction CH3CH2OCH2CH3, CHF2CF2OCH2CF3 with NO3 radical, showing that the reaction activity could be reduced due to the addition of fluorine atoms, which is further verified by the enthalpies, Gibbs free energies of the title reactions and C-H bond dissociation energies of the CH3CH2OCH2CH3, CHF2CF2OCH2CF3 and CF3CH2OCH3 molecules. The reaction thermodynamics and kinetics are determined, and the formation mechanisms of the products are proposed, which are crucial to determine the influence of CH3CH2OCH2CH3, CHF2CF2OCH2CF3 and CF3CH2OCH3 on air quality, as well as its atmospheric lifetime and durability. The atmospheric lifetimes of CH3CH2OCH2CH3, CHF2CF2OCH2CF3 and CF3CH2OCH3 are evaluated in the NO3-concentration range of 5 × 108-2 × 109 molecule cm-3 to fully consider the effects of different regions on their nocturnal migration. The radiation efficiency and global warming potentials (GWPs) have been reported. The products of title reaction CH3CH2OCHCH3, CF3CHOCF2CHF2 and CF3CHOCH3 are further oxidized into organic nitrates in the presence of O2 and NO. Organic nitrites can be isomerized into organic nitrates or degraded to form CH3C(O•)HOCH2CH3, CF3C(O•)HOCF2CHF2 and CH3C(O•)HOCF3 alkoxy radicals and NO2. This work provides deep insight into the night migration and transformation mechanism of the three ethers.

New insights into 3M3M1B: the role of water in ˙OH-initiated degradation and aerosol formation in the presence of NOX (X = 1, 2) and an alkali.

The oxidation mechanisms and dynamics of 3-methoxy-3-methyl-1-butanol (3M3M1B) initiated by ˙OH radicals were assessed by the density functional theory and canonical variational transition state theory. The effects of ubiquitous water on the title reactions were analyzed by utilizing an implicit solvation model in the present system. The results suggested that aqueous water played a negative role in the ˙OH-initiated degradation of 3M3M1B with an increase in the Gibbs free barriers. Meanwhile, the barriers were almost independent when explicit water molecules were involved in the gaseous phase, which could reduce the rate constant by approximately 3 orders of magnitude. The kinetic calculations showed that the rate constants were smaller by about 15, 9, 8, and 8 orders of magnitude for hydroxyl-, ammonia-, formic acid-, and sulfur acid-participating reactions, respectively, than that from an unassisted reaction. The results indicated that water, hydroxyl, ammonia, formic acid, or sulfur acid could not facilitate the title reaction when performed in the atmosphere. The investigations of the subsequent oxidation processes of the alkyl radical CH3OC(CH3)2CH2C·HOH indicated that CH3OC(CH3)2CH2CHO was the most favorable product by eliminating an HO2˙ radical. Additionally, the HO2˙ radical could serve as a self-catalyst to affect the above reaction through a double proton transfer process. With the introduction of NO, CH3OC(CH3)2CH2COOH and HNO2 were found to be the main products, which may be regarded as the new source of atmospheric nitrous acid. In the NO2-rich environment, the peroxynitrate of CH3OC(CH3)2CH2CH(OONO2)OH could be formed via the reaction of the CH3OC(CH3)2CH2CH(OO˙)OH radical with NO2. The degradation mechanism of CH3OC(CH3)2CH2CH(OONO2)OH in the presence of water, ammonia, and methylamine was demonstrated, and it was shown that water, ammonia, and methylamine could promote the formation of nitric hydrate and nitrate aerosol. The main species detected in the experiment were confirmed by a theoretical study. The atmospheric lifetimes of 3M3M1B in the temperature range of 217-298 K and altitude of 0-12 km were within the range of 6.83-8.64 h. This study provides insights into the transformation of 3M3M1B in a complex environment.

Computational exploration of regioselectivity and atmospheric lifetime in NO3-initiated reactions of CH3OCH3 and CH3OCH2CH3.

The NO3-initiated reactions of CH3OCH3 and CH3OCH2CH3 have been investigated by the BHandHLYP method in conjunction with the 6-311G(d,p) basis set. Thermodynamic and kinetic data are further refined using the comparatively accurate CCSD(T) method. According to the values of reaction enthalpies (ΔHr,298θ) and reaction Gibbs free energies (ΔGr,298θ) from CH3OCH2CH3 with NO3 system, we find that H-abstraction pathway from the α-CH2 group is more exothermic. It is further confirmed by the calculated CH bond dissociation energy of CH3OCH2CH3 molecule. All the rate constants, computed through means of canonical variational transition state with small-curvature tunneling correction, are fitted to the three-parameter expressions k1=1.54×10-23T3.34exp(-1035.53/T) and k2=3.55×10-26T4.31exp(-281.24/T)cm3molecule-1s-1 and branching ratios are computed over the temperature range 200-600K. The branching ratios are also discussed. The atmospheric lifetimes of CH3OCH3 and CH3OCH2CH3 determined by the NO3 radical are about 270 and 29days, respectively.

Theoretical insight into OH- and Cl-initiated oxidation of CF3OCH(CF3)2 and CF3OCF2CF2H &fate of CF3OC(X•)(CF3)2 and CF3OCF2CF2X• radicals (X=O, O2).

In this study, the mechanistic and kinetic analysis for reactions of CF3OCH(CF3)2 and CF3OCF2CF2H with OH radicals and Cl atoms have been performed at the CCSD(T)//B3LYP/6-311++G(d,p) level. Kinetic isotope effects for reactions CF3OCH(CF3)2/CF3OCD(CF3)2 and CF3OCF2CF2H/CF3OCF2CF2D with OH and Cl were estimated so as to provide the theoretical estimation for future laboratory investigation. All rate constants, computed by canonical variational transition state theory (CVT) with the small-curvature tunneling correction (SCT), are in reasonable agreement with the limited experimental data. Standard enthalpies of formation for the species were also calculated. Atmospheric lifetime and global warming potentials (GWPs) of the reaction species were estimated, the large lifetimes and GWPs show that the environmental impact of them cannot be ignored. The organic nitrates can be produced by the further oxidation of CF3OC(•)(CF3)2 and CF3OCF2CF2• in the presence of O2 and NO. The subsequent decomposition pathways of CF3OC(O•)(CF3)2 and CF3OCF2CF2O• radicals were studied in detail. The derived Arrhenius expressions for the rate coefficients over 230-350 K are: k T(1) = 5.00 × 10-24T3.57 exp(-849.73/T), k T(2) = 1.79 × 10-24T4.84 exp(-4262.65/T), kT(3) = 1.94 × 10-24 T4.18 exp(-884.26/T), and k T(4) = 9.44 × 10-28T5.25 exp(-913.45/T) cm3 molecule-1 s-1.

Understanding the insight into the mechanisms and dynamics of the Cl-initiated oxidation of (CH3)3CC(O)X and the subsequent reactions in the presence of NO and O2 (X = F, Cl, and Br).

In this work, the density functional and high-level ab initio theories are adopted to investigate the mechanisms and kinetics of reaction of (CH3)3CC(O)X (X = F, Cl, and Br) with atomic chlorine. Rate coefficients for the reactions of chlorine atom with (CH3)3CC(O)F (k1), (CH3)3CC(O)Cl (k2), and (CH3)3CC(O)Br (k3) are calculated using canonical variational transition state theory coupled with small curvature tunneling method over a wide range of temperatures from 250 to 1000 K. The dynamic calculations are performed by the variational transition state theory with the interpolated single-point energies method at the CCSD(T)/aug-cc-pVDZ//B3LYP/6-311++G(d,p) level of theory. Computed rate constant is in good line with the available experimental value. The rate constants for the title reactions are in this order: k1

Theoretical Study of the Gaseous Hydrolysis of NO2 in the Presence of Amines.

The effects on the hydrolysis of NO2 in the presence of methylamine and dimethylamine molecules were investigated by theoretical calculations of a series of the molecular clusters 2NO2-mH2O-CH3NH2 (m = 1-3) and 2NO2-mH2O-(CH3)2NH (m = 1, 2). With methylamine included in the clusters, the energy barrier is reduced by 3.2 kcal/mol from that with ammonia, and the corresponding products may form without an energy barrier. The results show that amines have larger effects than ammonia in promoting the hydrolysis of NO2 on thermodynamics. The additional water molecules can stabilize the transition states and the product complexes, and we infer that adding more water molecules in the reactions mainly act as solvent and promoting to form the methylamine nitrate (CH3NH3+NO3-). In addition, the interactions of CH3NH2 and (CH3)2NH on the hydration of HNO3 are also more effective than NH3, and the NH4NO3, CH3NH3NO3, and (CH3)2NH2NO3 complexes tend to form the larger aerosols with the increasing of water molecules. The equilibrium geometries, harmonic vibrational frequencies, and intensities of both HONO-CH3NH2 and HONO-NH3 complexes were investigated. Calculations predict that the binding energies of both HONO-CH3NH2 complexes are larger than HONO-NH3 complexes, and the OH stretching vibrational frequencies and intensities are most affected. The natural bond orbital analysis was performed to describe the donor-acceptor interactions on a series of complexes in the reactions 2NO2 + H2O + CH3NH2 and 2NO2 + H2O + (CH3)2NH, as well as the complexes of HONO-NH3 and HONO-CH3NH2. The results show that the interactions with amines are relatively larger, and the higher stabilization energies between CH3NH2 and HONO are found.

Computational study of H-abstraction reactions from CH3OCH2CH2Cl/CH3CH2OCH2CH2Cl by Cl atom and OH radical and fate of alkoxy radicals.

Multichannel gas-phase reactions of CH3OCH2CH2Cl/CH3CH2OCH2CH2Cl with chlorine atom and hydroxyl radical have been investigated using ab initio method and canonical variational transition-state dynamic computations with the small-curvature tunneling correction. Further energetic information is refined by the coupled-cluster calculations with single and double excitations (CCSD)(T) method. Both hydrogen abstraction and displacement processes are carried out at the same level. Our results reveal that H-abstraction from the -OCH2- group is the dominant channel for CH3OCH2CH2Cl by OH radical or Cl atom, and from α-CH2 of the group CH3CH2- is predominate for the reaction CH3CH2OCH2CH2Cl with Cl/OH. The contribution of displacement processes may be unimportant due to the high barriers. The values of the calculated rate constants reproduce remarkably well the available experiment data. Standard enthalpies of formation for reactants and product radicals are calculated by isodesmic reactions. The Arrhenius expressions are given within 220-1200 K. The atmospheric lifetime, ozone depleting potential (ODP), ozone formation potential (OFP), and global warming potential (GWP) of CH3OCH2CH2Cl/CH3CH2OCH2CH2Cl are investigated. Meanwhile, the atmospheric fate of the alkoxy radicals are also researched using the same level of theory. To shed light on the atmospheric degradation, a mechanistic study is obtained, which indicates that reaction with O2 is the dominant path for the decomposition of CH3OCH(O•)CH2Cl, the C-C bond scission reaction is the primary reaction path in the consumption of CH3CH(O•)OCH2CH2Cl in the atmosphere. HIGHLIGHTS: Ab initio method and canonical variational transition-state theory are employed to study the kinetic nature of hydrogen abstraction reactions of CH3OCH2CH2Cl/CH3CH2OCH2CH2Cl with Cl atom and OH radical and fate of alkoxy radicals (CH3OCH(O•)CH2Cl/CH3CH(O•)OCH2CH2Cl).

Theoretical Studies of the Reactions CFx H3-x COOR+Cl and CF3 COOCH3 +OH.

The mechanism and kinetics of the reactions of CF(3)COOCH(2)CH(3), CF(2)HCOOCH(3), and CF(3)COOCH(3) with Cl and OH radicals are studied using the B3LYP, MP2, BHandHLYP, and M06-2X methods with the 6-311G(d,p) basis set. The study is further refined by using the CCSD(T) and QCISD(T)/6-311++G(d,p) methods. Seven hydrogen-abstraction channels are found. All the rate constants, computed by a dual-level direct method with a small-curvature tunneling correction, are in good agreement with the experimental data. The tunneling effect is found to be important for the calculated rate constants in the low-temperature range. For the reaction of CF(3)COOCH(2)CH(3) +Cl, H-abstraction from the CH(2) group is found to be the dominant reaction channel. The standard enthalpies of formation for the species are also calculated. The Arrhenius expressions are fitted within 200-1000 K as kT(1) =8.4×10(-20) T (2.63) exp(381.28/T), kT(2) =2.95×10(-21) T (3.13) exp(-103.21/T), kT(3) =1.25×10(-23) T (3.37) exp(791.98/T), and kT(4) =4.53×10(-22) T (3.07) exp(465.00/T).

Theoretical study on the reactions of (CF3)2CFOCH3 + OH/Cl and reaction of (CF3)2CFOCHO with Cl atom.

Reactions of (CF3)2CFOCH3 and (CF3)2CFOCHO with hydroxyl radical and chlorine atom are studied at the B3LYP and BHandHLYP/6-311+G(d,p) levels along with the geometries and frequencies of all stationary points. This study is further refined by CCSD(T) and QCISD(T)/6-311+G(d,p) methods in the minimum energy paths. For the reaction (CF3)2CFOCH3 + OH, two hydrogen abstraction channels are found. The total rate constants for the reactions (CF3)2CFOCH3 + OH/Cl and (CF3)2CFOCHO + Cl are followed by means of the canonical variational transition state with the small-curvature tunneling correction. The comparison between the hydrogen abstraction rate constants by hydroxyl and chlorine atom is discussed. Calculated rate constants are in reasonable agreement with the available experiment data. The standard enthalpies of formation for the reactants, (CF3)2CFOCH3 and (CF3)2CFOCHO, and two products, (CF3)2CFOCH2 and (CF3)2CFOCO, are evaluated by a series of isodesmic reactions. The Arrhenius expressions for the title reactions are given as follows: k1= 1.08 × 10(-22) T(3.38) exp(-213.31/T), k2= 3.55 × 10(-22) T(3.61) exp(-240.26/T), and k3= 3.00 × 10 (-19) T(2.58) exp(-1294.34/T) cm(3) molecule(-1) s(-1).

The V-shaped polar molecules encapsulated into Cs (10528)-C72: stability and nonlinear optical response.

Recently, a new sulfide cluster fullerene, Sc2S@Cs (10528)-C72 containing two pairs of fused pentagons has been isolated and characterized (Chen et al., J. Am. Chem. Soc., 2012, 134, 7851). Inspired by this investigation, we propose a question: what properties will be influenced by the interaction between the encapsulated V-shaped polar molecule and C72? To answer this question, four encapsulated metallic fullerenes (EMFs) M2N@C72 (M = Sc or Y, N = S or O) along with pristine Cs-C72 (10528) were investigated by quantum chemistry methods. The results show that the Egap (3.01-3.14 eV) of M2N@C72 are significantly greater than that of pristine Cs-C72 (10528) (2.34 eV). This indicates that the stabilities of these EMFs increase by encapsulating the V-shaped polar molecule into the fullerene. Furthermore, the natural bond orbital (NBO) charge analysis indicates electron transfer from M2N to C72 cage, which plays a crucial role in enhancing first hyperpolarizability (ßtot). The ßtot follows the order of 1174 au (Y2O@C72) ≈ 1179 au (Sc2O@C72) > 886 au (Y2S@C72) ≈ 864 au (Sc2S@C72) > 355 au (C72). This indicates that the ßtot of M2N@C72 is more remarkable than that of pristine Cs-C72 (10528) due to the induction effect of the encapsulated molecule. Compared with sulfide cluster fullerenes (Y2S@C72 and Sc2S@C72), oxide cluster fullerenes (Sc2O@C72 and Y2O@C72) show much larger ßtot due to the small ionic radius and the large electronegativity of oxygen. In contrast, the metal element (scandium and yttrium) has a slight influence on the ßtot. Thus, oxide cluster fullerenes are candidates to become promising nonlinear optical materials with higher performance.

Computational studies on the mechanism and kinetics of Cl reaction with C2H5I.

The dual-level direct kinetics method has been used to investigate the multichannel reactions of C(2)H(5)I + Cl. Three hydrogen abstraction channels and one displacement process are found for the title reaction. The calculation indicates that the hydrogen abstraction from -CH(2)- group is the dominant reaction channel, and the displacement process may be negligible because of the high barrier. The rate constants for individual reaction channels are calculated by the improved canonical variational transition-state theory with small-curvature tunneling correction over the temperature range of 220-1500 K. Our results show that the tunneling correction plays an important role in the rate constant calculation in the low-temperature range. Agreement between the calculated and experimental data available is good. The Arrhenius expression k(T) = 2.33 x 10(-16) T(1.83) exp(-185.01/T) over a wide temperature range is obtained. Furthermore, the kinetic isotope effects for the reaction C(2)H(5)I + Cl are estimated so as to provide theoretical estimation for future laboratory investigation.