Yunju Zhang

Mechanistic and Kinetic Study of CH2O+O3 Reaction

Both singlet and triplet potential energy surfaces for the reaction of ground-state formaldehyde (CH(2)O) and ozone (O(3)) are theoretically investigated at the BMC-CCSD//BHandHLYP/6-311+G(d,p) level. Various possible isomerization and dissociation pathways are probed. Hydrogen abstraction, oxygen abstraction, and C-addition/elimination are found on both the singlet and the triplet surfaces. The major products for the total reaction are HCO and HOOO, which are generated via hydrogen abstraction. The transition state theory (TST) and multichannel RRKM calculations have been carried out for the total and individual rate constants for determinant channels over a wide range of temperatures and pressures.

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.

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 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 electronic structure and optical properties of carbazole-π-dimesitylborane as bipolar fluorophores for nondoped blue OLEDs

Molecules with D-π-A structures are drawing increased attention for applications in organic electronic devices due to their distinct optoelectronic properties. A study of a new series of bipolar fluorophores that have been chemically modified for use as highly efficient nondoped blue organic light-emitting diodes (OLEDs) has been carried out based on existing molecular structures and a literature survey. The aim of this study is to provide a profound interpretation of the optical and electronic properties and the structure-property relationships of a series of new bipolar fluorophores. The study also aims to predict the photophysical and optoelectronic properties of the new fluorophores. The density functional theory (DFT) has been confirmed as reliable, especially in predicting the properties of unknown products. The geometry and the electronic structure of these molecules in the ground state were studied with DFT and ab initio HF, whereas the lowest singlet excited-state geometries were optimized by ab initio singlet configuration interaction (CIS). The absorption and emission spectra, both in the gas phase and in THF, and the lowest singlet excited energies were calculated by employing the time-dependent density functional theory (TDDFT) and the polarizable continuum model (PCM). To precisely predict the charge-transporting and charge-confining properties of the new fluorophores, three-layered devices have been simulated. The results show that the molecular geometries, HOMOs, LUMOs, energy gaps, ionization potentials (IP), electron affinities (EA), radiative lifetimes (τ), absorption and emission spectra are all tuned by chemical modifications with different π-conjugated bridges. The results also show that these molecular materials could be used as bipolar light-emitting materials for blue and deep-blue OLEDs.

Mechanism and kinetic study of 3-fluoropropene with hydroxyl radical reaction.

Potential energy surface for the reaction of hydroxyl radical (OH) with 3-fluoropropene (CH₂CHCH₂F) has been studied to evaluate the reaction mechanisms, possible products and rate constants. It has been shown that the CH₂CHCH₂F with OH reaction takes place via a barrierless addition/elimination and hydrogen abstraction mechanism. It is revealed for the first time that the initial step for the barrierless additional process involves a pre-reactive loosely bound complex (CR1) that is 1.60 kcal/mol below the energy of the reactants. Subsequently, the reaction bifurcates into two different pathways to form IM1 (CH₂CHOHCH₂F) and IM2 (CH₂OHCHCH₂F), which can decompose or isomerize to various products via complicated mechanisms. Variational transition state model and multichannel RRKM theory are employed to calculate the temperature-, pressure-dependent rate constants and branching ratios. At atmospheric pressure with He as bath gas, IM1 formed by collisional stabilization is dominated at T≤600 K; whereas the direct hydrogen abstraction leading to CH₂CHCHF and H₂O are the major products at temperatures between 600 and 3000 K, with estimated contribution of 72.9% at 1000 K. Furthermore, the predicted rate constants are in good agreement with the available experimental values.

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

The reaction of propargyl alcohol with hydroxyl radical has been studied extensively at CCSD(T)/aug‐cc‐pVTZ//MP2/cc‐pVTZ level. This is the first time to gain a conclusive insight into the reaction mechanism and kinetics for this important reaction in detail. Two reaction mechanisms were revealed, namely addition/elimination and hydrogen abstraction mechanism. The reaction mechanism confirms that OH addition to CC triple bond forms the chemically activated adducts, IM1 (·CHCOHCH2OH) and IM2 (CHOH·CCH2OH), and the hydrogen abstraction pathways (CH2OH bonded to the carbon atom and alcohol hydrogen) may occur via low barriers. Harmonic model of Rice–Ramsperger–Kassel–Marcus theory and variational transition state theory are used to calculate the overall and individual rate constants over a wide range of temperatures and pressures. The calculated rate constants are in good agreement with the experimental data. At atmospheric pressure with Ar as bath gas, IM1 (·CHCOHCH2OH) and IM2 (CHOH·CCH2OH) formed by collisional stabilization are dominant in the low temperature range. The production of CHCCHOH + H2O via hydrogen abstraction becomes dominate at higher temperature. The fraction of IM3 (CH2COHCH2·O) is very significant over the moderate temperature range.

The mechanistic study of the hydroxyl radical reaction with trans-2-chlorovinyldichloroarsine

The trans-2-chlorovinyldichloroarsine (Lewisite) was produced and handled during WWI and WWII as chemical warfare agents. It was very difficult to explore its chemical characterization by experiments ways. The quantum chemical calculations proved to be a precise and harmless method for the toxicological system. In this paper, the gas phase reaction mechanisms of OH radical with trans-2-chlorovinyldichloroarsine (lewisite) were studied by second-order Møller–Plesset perturbation theory (MP2) method. The geometries of reactants, products, complexes, and transition states were optimized at the MP2/6-311++G(d,p) level. To gain more accurate mechanistic knowledge, the single-point energies were calculated using G3 and CCSD(T) method. This reaction exhibited three mechanisms, namely, direct hydrogen abstraction, direct chlorine abstraction, and addition/elimination. Multichannel Rice–Ramsperger–Kassel–Marcus theory and transition-state theory have been carried out for overall and individual rate constants over a wide range of temperatures and pressures. The computational results indicated that addition/elimination reaction is more favorable than direct hydrogen abstraction and direct chlorine abstraction. The major products for the total reaction are AsCl2 and CHClCH2O generated via C(2)-addition/elimination.

The atmospheric degradation pathways of BrCH2O2: computational calculation on mechanisms of the reaction with HO2.

Mechanisms for the atmospheric degradation reaction of BrCH2O2+HO2 were investigated using quantum chemistry methods. The result indicates that the dominant product is BrCH2OOH+O2((3)Σ). While CH2O+HBr+O3, BrCHO+OH+HO2 and CH2O+Br+HO3 will be competitive to a certain extent in the atmosphere. Meanwhile, the nascent product - BrCH2OOH reacts easily with OH radicals leading to BrCH2O2 again under the atmospheric conditions. Moreover, OH radicals could act as a catalyst in the net reaction of BrCH2OOH→BrCHO+H2O. Thus the proposed product BrCHO+H2O+O2 in the experiment might be generated from the subsequent reaction of BrCH2OOH with extra OH radicals. Comparisons indicate that halogen substitution effect makes minor contributions to the XCH2O2 (X=H, F, Cl and Br)+HO2 reactions in the atmosphere.

A quantum chemical study on ˙Cl-initiated atmospheric degradation of acrylonitrile

Degradation of acrylonitrile (CH2CHCN) by reaction with atomic chlorine was studied using quantum chemical methods. Density functional theory (DFT) (B3LYP, BHandHLYP, M11, MN12SX, M05-2X, and M06-2X) and Moller–Plesset perturbation theory (MP2) with the same basis set 6-311++G(d,p) were employed to obtain the geometries of intermediates and transition states. Potential energy surfaces (PESs) were characterized at the UCCSD(T)/cc-PVTZ//M05-2X/6-311++G(d,p) level. The dominant channel is the formation of the intermediate IM1(CH2ClCHCN) by barrierless addition between ˙Cl and the terminal carbon atom of the CC double bond of acrylonitrile. Direct hydrogen-abstraction channels are negligible because of higher barriers and the endothermic process. The calculated rate constants were followed by means of the variational transition state theory by Variflex code, and these were in good agreement with the experimental values. The subsequent and secondary reactions for IM1(CH2ClCHCN) involving NO and O2 molecules were also investigated in the atmosphere. The atmospheric lifetime of acrylonitrile in ˙Cl is about 18 h in the marine boundary layer. The contribution of ˙Cl to the transformation of acrylonitrile is comparative with that of the ˙OH. Thus, it is necessary to consider ˙Cl initiated tropospheric degradation of acrylonitrile.