Yizhen Tang

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 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.

Theoretical Investigations on Mechanisms and Pathways of C2H5O2 with BrO Reaction in the Atmosphere

In this work, feasible mechanisms and pathways of the C2H5O2 + BrO reaction in the atmosphere were investigated using quantum chemistry methods, i.e., QCISD(T)/6-311++G(2df,2p)//B3LYP/6-311++G(2df,2p) levels of theory. Our result indicates that the title reaction occurs on both the singlet and triplet potential energy surfaces (PESs). Kinetically, singlet C2H5O3Br and C2H5O2BrO were dominant products under the atmospheric conditions below 300 K. CH3CHO2 + HOBr, CH3CHO + HOBrO, and CH3CHO + HBrO2 are feasible to a certain extent thermodynamically. Because of high energy barriers, all products formed on the triplet PES are negligible. Moreover, time-dependent density functional theory (TDDFT) calculation implies that C2H5O3Br and C2H5O2BrO will photolyze under the sunlight.

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.