Theoretical study on the mechanisms, kinetics and risk assessment of OH radicals and Cl atom initiated transformation of HCFC-235fa in the atmosphere.

Hydrochlorofluorocarbons (HCFCs) are important greenhouse gases and ozone-depleting substances. Thus, a thorough understanding of their atmospheric fate is essential for preventing and controlling atmospheric pollution. Herein, the atmospheric transformation mechanism of CF3CH2CClF2 (HCFC-235fa) by the OH radical and the Cl atom was carried out at the dual-level of CCSD(T)/aug-cc-pVTZ//M06-2X/6-311+G(d,p). The reaction rate coefficients were calculated using the multistructural canonical variational transition state theory with small curvature tunneling (MS-CVT/SCT) at 200-1000 K. The kMS-CVT/SCT(CF3CH2CClF2 + OH) and kMS-CVT/SCT(CF3CH2CClF2 + Cl) values are 9.05 × 10-15 and 1.95 × 10-17 cm3 molecule-1 s-1 at 297 K, respectively. The results show that the role of OH is more important than Cl in the degradation of CF3CH2CClF2. The atmospheric lifetimes (83 days-77.93 years), ozone destruction potential (0.001-0.023), and global warming potentials (GWP100 = 21.06-5157.35) of CF3CH2CClF2 were assessed, and these results indicate that CF3CH2CClF2 is atmospherically persistent and environmentally unfriendly. The evolution mechanisms of CF3C·HCClF2, CF3C(OO˙)HCClF2, and CF3C(O˙)HCClF2 in the presence of O2, HO2˙, and NO were investigated and discussed. The resulting products of CF3CH2CClF2 are mostly highly oxidized multi-functional compounds in the forms of aldehydes, ketones, and organic nitrates. A computational assessment of acute and chronic toxicities was performed at three levels of nutrition in order to improve the understanding of the potential toxicity of CF3CH2CClF2 and its degradation products to the aquatic environment. The acidification potential of CF3CH2CClF2 was calculated to be 1.141 and presumed to contribute to the formation of acid rain. The results may contribute to describing HCFCs' atmospheric fate, persistence, and environmental risks.

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.

Interaction of Glutamic Acid/Protonated Glutamic Acid with Amide and Water Molecules: A Theoretical Study.

Amino acids are important nitrogen-containing compounds and organic carbon components that exist widely in the atmosphere. The formation of atmospheric aerosols is affected by their interactions with amides. The dimers formed by glutamic acid (Glu) or protonated glutamic acid (Glu+) with three kinds of amide molecules (formamide FA, acetamide AA, urea U) and the hydrated clusters formed by Glu or Glu+, U molecules along with one to six water molecules were systematically studied at the M06-2X/6-311++G(3df,3pd) level. U is predicted to form a more stable structure with Glu/Glu+ than FA and AA by thermodynamics. If the concentration ratio of FA to U is less than 104, U will play a critical role in NPF. The degree of hydration in Glu+-mU-nW is higher than that of Glu-mU-nW (m = 0, 1; n = 0-6) clusters. Notably, Glu contributes more to the Rayleigh scattering properties than glutaric acid and sulfuric acid, and thus may lead to the destruction of atmospheric visibility. This study is helpful to better understand the properties of organic aerosols containing amino acids or amides.

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.

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.

Unveiling the Photophysical Properties of Boron Heptaaryldipyrromethene Derivatives.

Increased interest has been devoted to the discovery of multifunctional materials with desirable properties, as continuous performance enhancement of various devices mainly depends on high-performance materials. Now, density functional theory has become a powerful tool to design new materials and rationalize experimental observations. In this work, we explored the photophysical properties origin of chiral boron heptaaryldipyrromethene (heptaaryl-BODIPY), which has charming optoelectronic properties. At the same time, we designed the other five compounds on the basis of heptaaryl-BODIPY. The simulated electronic absorption and emission spectra of heptaaryl-BODIPY are in agreement with experimental ones, allowing us to reliably assign its electronic transition property. The designed compound 6 shows remarkably large first hyperpolarizability value up to 82.78×10-30  esu. For this kind of compounds, their NLO response values associate with not only position but also electronic nature of substituent groups. Moreover, electron reorganization energies of compounds 1-4 are comparable to tris(8-hydroxyquinolinato)aluminium(III) which is a typical electron transport material. Intriguingly, the studied compounds are the excellent fluorescent probe materials from the standpoint of large Stokes shift and high emission efficiency. Our work enables an opportunity for understanding the relationship between microelectronic structure and macroscopic performance of BODIPY derivatives.

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.

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).

Theoretical study on the gas phase reaction of allyl chloride with hydroxyl radical.

The reaction of allyl chloride with the hydroxyl radical has been investigated on a sound theoretical basis. This is the first time to gain a conclusive insight into the reaction mechanism and kinetics for important pathways in detail. The reaction mechanism confirms that OH addition to the C=C double bond forms the chemically activated adducts, IM1 (CH2CHOHCH2Cl) and IM2 (CH2OHCHCH2Cl) via low barriers, and direct H-abstraction paths may also occur. Variational transition state model and multichannel RRKM theory are employed to calculate the temperature-, pressure-dependent rate constants. The calculated rate constants are in good agreement with the experimental data. At 100 Torr with He as bath gas, IM6 formed by collisional stabilization is the major products in the temperature range 200-600 K; the production of CH2CHCHCl via hydrogen abstractions becomes dominant at high temperatures (600-3000 K).

Theoretical study on the gas phase reaction of allyl alcohol with hydroxyl radical.

The complex potential energy surface of allyl alcohol (CH2CHCH2OH) with hydroxyl radical (OH) has been investigated at the G3(MP2)//MP2/6-311++G(d,p) level. On the surface, two kinds of pathways are revealed, namely, direct hydrogen abstraction and addition/elimination. Rice-Ramsperger-Kassel-Marcus theory and transition state theory are carried out to calculate the total and individual rate constants over a wide temperature and pressure region with tunneling correction. It is predicted that CH2CHOHCH2OH (IM1) formed by collisional stabilization is dominate in the temperature range (200-440 K) at atmospheric pressure with N2 (200-315 K at 10 Torr Ar and 100 Torr He). The production of CH2CHCHOH + H2O via direct hydrogen abstraction becomes dominate at higher temperature. The kinetic isotope effect (KIE) has also been calculated for the title reaction. Moreover, the calculated rate constants and KIE are in good agreement with the experimental data.

Theoretical studies on the mechanisms and dynamics of OH radical with (CH3)3COOH and (CH3)2CHOOH.

A dual-level direct dynamic method is employed to study the reaction mechanism of hydroxyl radical with (CH(3))(3)COOH and (CH(3))(2)CHOOH. Eight hydrogen abstraction channels are found for title reactions. The energy paths are optimized at the BH&H-HLYP/6-311G(d,p) level, and the energy profiles are further refined by interpolated single-point energies method at the CCSD(T) and QCISD(T) theories. Rate coefficients for the reactions of the OH with (CH(3))(3)COOH/(CH(3))(2)CHOOH are computed by the canonical variational transition-state theory with the small-curvature tunneling correction between 200 and 2000 K. The Arrhenius expressions k(1) (T) = 1.49 × 10(-26) T(4.71) exp(1981.92/T) and k(2) (T) = 1.58 × 10(-20) T(3.32) exp(210.59/T) over 200-2000 K are obtained.

Mechanistic and kinetic study of CF3CH═CH2 + OH reaction.

The potential energy surfaces of the CF(3)CH═CH(2) + OH reaction have been investigated at the BMC-CCSD level based on the geometric parameters optimized at the MP2/6-311++G(d,p) level. Various possible H (or F)-abstraction and addition/elimination pathways are considered. Temperature- and pressure-dependent rate constants have been determined using Rice-Ramsperger-Kassel-Marcus theory with tunneling correction. It is shown that IM1 (CF(3)CHCH(2)OH) and IM2 (CF(3)CHOHCH(2)) formed by collisional stabilization are major products at 100 Torr pressure of Ar and in the temperature range of T < 700 K (at P = 700 Torr with N(2) as bath gas, T ≤ 900 K), whereas CH(2)═CHOH and CF(3) produced by the addition/elimination pathway are the dominant end products at 700-2000 K. The production of CF(3)CHCH and CF(3)CCH(2) produced by hydrogen abstractions become important at T ≥ 2000 K. The calculated results are in good agreement with available experimental data. The present theoretical study is helpful for the understanding the characteristics of the reaction of CF(3)CH═CH(2) + OH.

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.

Theoretical study on the kinetics of OH radical reactions with CH3OOH and CH3CH2OOH.

The mechanisms and kinetics studies of the OH radical with alkyl hydroperoxides CH(3)OOH and CH(3)CH(2)OOH reactions have been carried out theoretically. The geometries and frequencies of all the stationary points are calculated at the UBHandHLYP/6-311G(d,p) level, and the energy profiles are further refined by interpolated single-point energies method at the MC-QCISD level of theory. For two reactions, five H-abstraction channels are found and five products (CH(3)OO, CH(2)OOH, CH(3)CH(2)OO, CH(2)CH(2)OOH, and CH(3)CHOOH) are produced during the above processes. The rate constants for the CH(3)OOH/CH(3)CH(2)OOH + OH reactions are corrected by canonical variational transition state theory within 250-1500 K, and the small-curvature tunneling is included. The total rate constants are evaluated from the sum of the individual rate constants and the branching ratios are in good agreement with the experimental data. The Arrhenius expressions for the reactions are obtained.

Synergistic effect of glutaric acid and ammonia/amine/amide on their hydrates in the clustering: A theoretical study.

The formation of molecular clusters makes influence on the atmosphere. The clusters of glutaric acid (GA) and common ammonia (A), amine (methylamine MA, dimethylamine DMA) and representative amide (urea U) along with water molecule were systematically studied theoretically. GA-A-nW (n = 1, 2), GA-MA-nW (n = 1, 2), GA-DMA-1W and GA-U-nW (n = 1-6) are predicted to be feasible thermodynamically with the hydrogen bonds as interaction force. GA and urea promote the clustering synergistically, and ammonia, methylamine, dimethylamine promote the clustering of small GA hydrates (n = 1-2), while inhibit that of large GA hydrates (n = 3-6). The results of humidity show that un-hydrate or mono-hydrate is the main form of GA-mbase-nW (m = 0, 1; n = 1-6) under relative humidity of 20%, 50% and 80%. The global minima remain dominant over the temperature range of 220-320 K. GA contributes more to the Rayleigh scattering properties than sulfuric acid. More importantly, the local minima can undergo isomerization to form the global minima crossing a free energy barrier ranging from 6.66 to 11.78 kcal mol-1. This study indicates that GA and base molecules play a synergistic role to promote the formation of clusters. We hope it can provide more insights on interesting clustering in theory.

Mechanistic and kinetic investigations of N2H4 + OH reaction.

The reaction of N(2)H(4) with OH has been investigated by quantum chemical methods. The results show that hydrogen abstraction mechanism is more feasible than substitution mechanism thermodynamically. The calculated rate constants agree with the available experimental data. The calculated results show that the variational effect is small at lower temperature region, while it becomes significant at higher temperature region. On the other hand, the small-curvature tunneling effect may play an important role in the temperature range 220-3000 K. Moreover, the calculated rate constants show negative temperature dependence at the temperatures below 500 K, which is in accordance with Vaghjiani's report that slightly negative temperature dependence is found over the temperature range of 258-637 K. The mechanism of the major product (N(2)H(3)) with OH has also been investigated theoretically to understand the title reaction thoroughly.

Theoretical and kinetic study of the H + C2H5CN reaction.

The reaction of H radical with C(2)H(5)CN has been studied using various quantum chemistry methods. The geometries were optimized at the B3LYP/6-311+G(d,p) and B3LYP/6-311++G(2d,2p) levels. The single-point energies were calculated using G3 and BMC-CCSD methods based on B3LYP/6-311++G(2d,2p) geometries. Four mechanisms were investigated, namely, hydrogen abstraction, C-addition/elimination, N-addition/elimination and substitution. The kinetics of this reaction were studied using the transition state theory and multichannel Rice-Ramsperger-Kassel-Marcus methodologies over a wide temperature range of 200-3000 K. The calculated results indicate that C-addition/elimination channel is the most feasible over the whole temperature range. The deactivation of initial adduct C(2)H(5)CHN is dominant at lower temperature with bath gas H(2) of 760 Torr; whereas C(2)H(5)+HCN is the dominant product at higher temperature. Our calculated rate constants are in good agreement with the available experimental data.