Photodegradation of butyl acrylate in the troposphere by OH radicals: kinetics and fate of 1,2‐hydroxyalcoxy radicals

The rate constant of the reaction of OH radicals with butyl acrylate was studied for the first time using an atmospheric simulation chamber at 298 K and ～750 Torr of air or nitrogen. The decay of the organics was followed using a gas chromatograph with a flame ionization detector (GC‐FID), and the rate constant was determined using a relative rate method with different references. The obtained average value of (1.80 ± 0.26) × 10^?11 cm³ molecule^?1 s^?1 is in agreement with previous determinations of the rate constants of OH radicals with acrylates and methacrylates in the literature. Additionally, product identification under atmospheric conditions was performed for the first time by the GC‐MS technique. Butyl glyoxalate was observed as the degradation product in accordance with the addition of OH to the less substituted carbon atom of the double bond, followed by decomposition of the 1,2‐hydroxyalkoxy radicals formed. Room temperature rate coefficient was used to estimate the atmospheric lifetime of the ester studied. Reactivity trends are discussed in terms of the substituent effects and the length of the hydrogenated chain of the ester. The atmospheric persistence of BUAC was calculated taking into account the experimental rate constant obtained. Copyright © 2008 John Wiley & Sons, Ltd.     

Theoretical investigation of the oxidation pathways of the Cl-initiated reaction of 2-methyl-3-buten-2-ol

The mechanism and products of the reaction of 2-methyl-3-buten-2-ol (MBO232) with Cl atoms in the presence of O₂ have been elucidated by performing high-level quantum chemistry calculations. The geometries of the reactants, intermediates, transition states, and products are optimized at the MP2(full)/6-311G(d,?p) level, and their single-point energies are refined at the CCSD(T)/6-311?+?G(d,?p) level. The potential energy surface profiles have been constructed at the CCSD(T)/6-311?+?G(d,?p)//MP2(full)/6-311G(d,?p)?+?0.95?×?ZPE level of theory, and the possible channels involved in the reaction are also discussed. The calculations indicate that the reaction predominantly proceeds via the addition of Cl atoms to the double bond rather than the direct abstraction of the H atoms in MBO232. The nascent adducts (CH₃)₂C(OH)CHCH₂Cl (IM1) and (CH₃)₂C(OH)CHClCH₂ (IM2) do not undergo subsequent isomerization and dissociation reactions, but rather react with O₂. The theoretical results show that the major products are CH₂ClCHO and CH₃C(O)CH₃ for the reaction of MBO232?+?Cl in the presence of O₂, which is in good agreement with the experimental finding.     

CH,NH和OH自由基基态与低激发态分子结构与势能函数

用电子相关耦合簇方法CCSD(T)和aug-cc-pVTZ基函数计算研究了CH, NH和OH自由基分子基态与低激发态的结构与势能函数，导出了分子的光谱数据.结果表明，CH, NH和OH自由基分子基态分别为X²Π，X³Σ和X²Π，基态与低激发态的势能函数均可用Murrell-Sorbie function来表达.CH自由基分子低激发态a⁴Σ^－和⁶Σ^－的绝热 关键词： 电子相关耦合方法 势能函数 结构 自由基     

Theoretical studies on atmospheric chemistry of HFE‐347mcc3: reactions with OH radicals and Cl atoms

Detailed theoretical investigation has been performed on the mechanism, kinetics and thermochemistry of the gas phase reactions of CF₃CF₂CF₂OCH₃ (HFE‐347mcc3) with OH radicals and Cl atoms using M06‐2X/6‐31 + G(d,p) level of theory. Reaction profiles are modeled including the formation of pre‐reactive and post‐reactive complexes at entrance and exit channels, respectively. Using group‐balanced isodesmic reactions, the standard enthalpies of formation for species are also reported. The calculated bond dissociation energy for C―H bond is in good agreement with previous data. The rate constants of the two reactions are determined for the first time in a wide temperature range of 250–1000 K. At 298 K, the calculated rate coefficients are in good agreement with the experimental results. The atmospheric life time of HFE‐347mcc3 is estimated to be 4.4 years. Copyright © 2014 John Wiley & Sons, Ltd.     

Ar-H2(D2, T2)碰撞体系的振转相互作用势及散射截面的理论计算

用量子力学从头算的耦合族CCSD(T)方法, 使用相关一致基组aug-cc-pV5Z并加3s3p2d1f1g高斯键函数计算了Ar原子与H₂分子的振转相互作用和电荷分布, 采用Boys和Bernardi提出的均衡法消除了基组重叠误差(BSSE). 然后用Tang-Toennies势能函数拟合得到Ar-H₂体系相互作用势的解析表达式. 在该相互作用势下, 用密耦方法计算了Ar原子入射能量为83 meV时, Ar-H₂(D₂, T₂)碰撞体系的散射截面. 计算Ar-D₂体系的微分截面与实验值比较符合很好. 计算结果及分析表明, 在长程吸引势的散射中, 色散能起主要作用; 在短程排斥势的散射中, 交换能起重要作用. 当碰撞参数在0.27 nm至0.47 nm的范围时, Ar-H₂(D₂, T₂)碰撞体系的径向偶极发生两次转向.     

Theoretical mechanistic studies on the degradation of alizarin yellow R initiated by hydroxyl radical

The degradation of azo dyes has attracted many research efforts not only due to the resulting environmental problems but also because the azo compounds with various substituents may show different degradation mechanism. It has been computationally found here, for the first time, that the HO? initiated cleavages of C–N and N–N bonds of alizarin yellow R with carboxyl group are kinetically competitive. In view of the formation of HO? adducts, the C–N and N–N bond cleavages of the hydrazone tautomer of alizarin yellow R are also kinetically competitive, but the former is more thermodynamically favorable. This result is different from that previously reported for the hydrozone tautomers of Acid Orange 7 and Acid Orange 8 containing hydroxyl and azo groups in neighboring positions, which are favorable to follow C–N bond cleavage mechanism both kinetically and thermodynamically. The decarboxylation occurs via an attack of HO? to the benzene ring carbon connecting to the carboxyl group rather than a direct attack of HO? to the carboxyl carbon atom. The anion form has higher reactivity than the neutral form in all of the reactions investigated. In addition, a water molecule as a proton relay reagent could significantly reduce the energy barrier for the N–N bond cleavage of alizarin yellow R. Copyright © 2014 John Wiley & Sons, Ltd.     

Oxidation pathways in the reaction of diacetylene with OH radicals

We present a portion of the potential energy surface of the reaction of diacetylene with OH radicals, calculated using RQCISD(T) and two basis set extrapolation schemes. Based on this surface, we performed calculations of the rate coefficients using an RRKM/master-equation formalism. After a small (1 kcal/mol) adjustment to the energy barrier of the association reaction, our calculated rate coefficients of the high-pressure limit agree very well with previous direct measurements. However, our calculations at high temperatures are considerably smaller than the values inferred in previous studies. The non-Arrhenius behavior and significant pressure dependence of the rate coefficients above 800 K is due to the competition between stabilization, abstraction and addition-elimination channels. At low temperatures, the reaction proceeds mostly to the addition products, as well as to CO and propargyl. Above 1200 K, direct hydrogen abstraction and production of H atoms become important.     

Theoretical study of the helio hydrogen cyanide dication HeCNH2+

The structure and stability of the helio hydrogen cyanide molecular ion, HeCNH²⁺, is investigated by standard quantum chemical methods. Single reference calculations are carried out using second-order perturbation theory (MP2), the coupled cluster expansion in the CCSD approximation, and the hybrid approach using a perturbative estimate of the triple excitation energy component designated CCSD(T). Multireference calculations using a complete active space (CASSCF) and a second-order perturbation theory estimate of correlation effects (CASPT2) are reported.     

Ne-Xe体系势能曲线和光谱研究

本论文对Ne-Xe体系的势能曲线和束缚态能级作了系统的研究.采用耦合簇CCSD(T)方法和超分子近似,以及aug-cc-PVXZ(X=T,Q,5)基组,计算了Ne-Xe体系的相互作用势,并采用三种方案外推得到基底限值,给出了不同基底和外推方法下的势能曲线平衡位置和势阱深度.计算了Ne-Xe体系振转能级和各同位素基振动态的纯转动跃迁频率,及相应的光谱常数,并与实验结果进行了比较.     

Theoretical kinetic study on the decomposition of 1,5‐diaminotetrazole

1,5‐Daminotetrazole (DAT) is of much interest because of the practical significance and the diversity of characteristics. The study on the decomposition pathway and the kinetics of DAT has been performed based on the quantum chemistry theory. The minimum energy path (MEP) calculation has shown that NH₂N₃ and NH₂CN are the initially detected products of DAT. And the structures of reactant, products and transition state were optimized with MP2 methods using 6‐311G** basis sets, and the energies were refined using CCSD(T)/6‐311G** levels of theory. The calculated rate constants were obtained using the conventional transition‐state theory (TST) and the canonical variational transition‐state theory (CVT) methods. The calculation results indicated that the energy barrier of decomposition reaction is 47.98 kcal mol^?1 and the variational effect is small. In addition, the rate constants and the Arrhenius experience formula of DAT decomposition have been obtained between 200 and 2500 K temperature regions. The fitted three‐parameter expressions calculated using the TST and CVT methods are (TST) and (CVT). This work may provide the theoretical support for further experimental synthesis and testing. Copyright © 2015 John Wiley & Sons, Ltd.     

Theoretical study of efficiency of metal cations (Mg+, Ca+, and Ag+) for effective hydrogen storage

The interaction between the metal cations and H₂ molecule has been investigated using dispersion-corrected and -uncorrected hybrid density functional and CCSD(T) methods in conjunction with the correlation consistent triple-ζ quality basis sets for the storage of the H₂ molecule. The molecular properties, potential energy surfaces, stability, binding energy and well-depth have been computed for the metal cation–dihydrogen (M⁺–H₂, M = Mg, Ca, and Ag) complexes in the gas phase. The results obtained by the dispersion-corrected hybrid density functional B2PLYP-D method agree very well with the earlier experimental and theoretical results wherever available. Different components of the interaction energy have been estimated by the symmetry adapted perturbation theory (SAPT) to get physical insight into the interaction energy. Among the three complexes, only Ag⁺–H₂ is the most stable complex and it accumulates more H₂ molecules as the interaction between the metal cation Ag⁺ and the H₂ molecule is the greatest.     

Theoretical kinetics study of thymine tautomerism and interaction of Na+ with its tautomers

The current work is a theoretical study of the tautomerism of thymine in the gas phase. Eighteen structures were found in the isomerisation reaction of thymine, some of which are reported for the first time. Thirty hydrogen transfer reactions were carried out. In 24 of the reactions, the hydrogen abstractions N―H→O, N―H→C and C―H→O were considered. The potential energy surface for all trajectories was determined for 18 tautomers and 40 transition states. The RRKM-TST model was used to calculate the rate constants of the reactions to examine their kinetics. Nonlinear least-squares fitting was used to calculate the rate constants expressions. The interaction of sodium ion and tautomers in the gas phase was also investigated. Three types of interaction of metal cations with thymine were found. In the first, metal cations interact with a lone pair of nitrogen or oxygen tautomers. The second type is the interaction of metal cations with two nitrogen and oxygen of tautomers. The last type is the interaction of metal cations and the electron density of the π-system of thymine in which the metal ion is perpendicular to the ring of tautomers. The stability ranking of the thymine tautomers and their complexes was also determined.     

Theoretical investigation on kinetics and thermochemistry of reaction of CHF2CF2OCH2CF3 with OH radicals and global warming potentials

Theoretical investigation has been carried out on the mechanism, kinetics and thermochemistry of the gas-phase reactions between CHF₂CF₂OCH₂CF₃ and OH radical using a new hybrid density functional M06-2X/6-31+G(d,p) and G2(MP2)//M06-2X/6-31+G(d,p) methods. The most stable conformer of CHF₂CF₂OCH₂CF₃ is considered in our study and the possible H-abstraction reaction channels are identified. Each reaction channel shows an indirect H-abstraction reaction mechanism via the formation of pre-reactive complex. The rate coefficients are determined for the first time over a wide range of temperature 250–1000 K. At 298 K, the calculated total rate coefficient of k_OH = 1.01×10^?14 cm³ molecule^?1 s^?1 is in good agreement with the experimental results. The heats of formation for CHF₂CF₂OCH₂CF₃ and CF₂CF₂OCH₂CF₃ and CHF₂CF₂OCHCF₃ radicals are estimated to be -1739.25, -1512.93 and -1523.94 kJ mol^?1, respectively. The bond dissociation energies of the two C-H bonds are C(-H)F₂CF₂OCH₂CF₃: 423.34 kJ mol^?1 and CHF₂CF₂OC(-H)HCF₃: 411.87 kJ mol^?1. The atmospheric lifetime of CHF₂CF₂OCH₂CF₃ is estimated to be around 4.5 years and the 100-year time horizon global warming potentials of CHF₂CF₂OCH₂CF₃ relative to CO₂ is estimated to be 601.     

Lifetime of acyloxy radicals produced by decomposition of acetylpropionyl peroxide

The authors consider thermolysis of 0.5M solutions of acetylpropionyl peroxide in CCl₄ at 333 and 343 K as well as photolysis of 0.5M solutions of acetylpropinyl piroxide in CCl₄ at 253–333 K and photolysis of methanol solutions of acetylpropionyl peroxide with added 1 m CCl₄ at temperatures of 193–253 K. The effects of chemical nuclear polarization and reaction yields were analyzed to determine the decarboxylation rate constants of acyloxy radicals that were produced by thermolysis and photolysis of acetylplpropionyl peroxide. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 3, pp. 306–311. May–June, 1997.     

Theoretical study of the hydrogen abstraction reaction of CH3OH with NCO

A direct dynamics method is employed to study the mechanism and kinetics of the hydrogen abstraction reaction of CH₃OH with NCO. The optimized geometries and frequencies of the stationary points and the minimum-energy paths (MEPs) are obtained at the MP2/6-311G(d,p) level. In order to obtain more accurate potential energy surface (PES) information and provide more credible energy data for kinetic calculation, the single-point energies along the MEPs are further computed at QCISD(T)/6-311+G(d,p) and G3MP2 levels. The rate constants for two channels, the methyl-H abstraction channel and hydroxyl-H abstraction channel, are calculated by canonical variational transition state theory (CVT) with small-curvature tunneling (SCT) contributions over the wide temperature region 220–1500?K. The theoretical overall rate constants are in good agreement with the available experimental data. For the title reaction, the methyl-H abstraction channel is dominant, while the hydroxyl-H abstraction channel is negligible over the whole temperature region.     

On the convergence of zero-point vibrational corrections to nuclear shieldings and shielding anisotropies towards the complete basis set limit in water

ABSTRACT

The method and basis set dependence of zero-point vibrational corrections (ZPVCs) to nuclear magnetic resonance shielding constants and anisotropies has been investigated using water as a test system. A systematic comparison has been made using the Hartree–Fock, second-order Møller–Plesset perturbation theory (MP2), coupled cluster singles and doubles (CCSD), coupled cluster singles and doubles with perturbative triples corrections (CCSD(T)) and Kohn–Sham density functional theory with the B3LYP exchange-correlation functional methods in combination with the second-order vibrational perturbation theory (VPT2) approach for the vibrational corrections. As basis sets, the correlation consistent basis sets cc-pVXZ, aug-cc-pVXZ, cc-pCVXZ and aug-cc-pCVXZ with X = D, T, Q, 5, 6 and the polarisation consistent basis sets aug-pc-n and aug-pcS-n with n = 1, 2, 3, 4 were employed. Our results show that basis set convergence of the vibrational corrections is not monotonic and that very large basis sets are needed before a reasonable extrapolation to the basis set limit can be performed. Furthermore, our results suggest that coupled cluster methods and a decent basis set are required before the error of the electronic structure approach is lower than the inherent error of the VPT2 approximation.     

A computational perspective on the kinetics and thermochemistry of the gas phase reactions of 1, 1-dichlorodimethylether (DCDME) with OH radical at 298 K

Kinetics and thermochemistry of the gas phase reactions between CH₃OCHCl₂ (DCDME) and OH radical are investigated theoretically. The geometries and all the stationary points on the potential energy surface are calculated at BHandHLYP/6-311G(d,p) method. The energy information is further refined at CCSD(T)/6-311G(d,p) level of theory. Reaction profiles are modelled including the formation of two pre-reactive and post-complexes. The rate constants, which are evaluated by Canonical Transition State Theory (CTST) including tunnelling correction at 298 K, are in very good agreement with the available experimental data. The percentage contributions of both reaction channels are also reported at 298 K. The hydrogen abstraction reaction from the –CHCl₂ group is found to be dominant leading to the formation of CH₃OCCl₂ + H₂O. Using group-balanced isodesmic reactions, the standard enthalpies of formation for CH₃OCHCl₂, CH₃OCCl₂ and CH₂OCHCl₂ are also reported.     

(H2O)n (n=1-3)和H2SO4作用下H2CO3气相分解反应机理的理论研究

本文利用CCSD(T)/6-311++(3df,3pd)//B3LYP-D3/6-311++G(3df,3pd)+ 0.9686×ZPE理论方法对(H2O)n (n=1-3)和H2SO4存在与不存在的情况下,H2CO3气相分解反应机理进行了理论研究。计算结果表明(H2O)n (n=1-3)和H2SO4都能使H2CO3气相分解反应的能垒显著地降低,其催化能力按由强到弱的顺序是H2SO4>(H2O)2>(H2O)3>H2O。     

甲醇分子(CH3OH)光谱性质的理论计算

研究了气相甲醇分子(CH3OH)基态和激发态性质。在对不同方法基组所得计算结果和实验结果进行比较之后,选用MP2(full)/6-311++G(2d,2p)理论方法进行计算,得到甲醇分子(CH3OH)基态和三重激发态的几何结构、能量以及频率信息;频率计算显示基态和三重态都为稳定构型。从三重态的结构出发,解释了三重态势能面为排斥型势能面的合理性。计算了甲醇分子单重激发态的垂直激发能,比较不同方法不同基组计算的甲醇分子单重激发态的垂直激发能,发现用TDDFT 中的b3p86方法使用6-311++G**基组的计算值和实验值符合得最好。计算得到的甲醇分子在MP2(full)/6-311++G(2d,2p)的绝热电离能和垂直电离能分别为11.18eV和11.32eV;计算得到的绝热电子亲和势与垂直电子亲和势分别为0.888eV和0.893eV。计算结果对实验研究有指导意义。