Abstract
The mechanism and kinetics for the reaction of the HO2 radical with the ethyl (C2H5) radical have been investigated theoretically. The electronic structure information of the potential energy surface (PES) is obtained at the MP2/6-311++G(d,p) level of theory, and the single-point energies are refined by the CCSD(T)/6-311+G(3df,2p) level of theory. The kinetics of the reaction with multiple channels have been studied by applying variational transition-state theory (VTST) and Rice–Ramsperger–Kassel–Marcus (RRKM) theory over wide temperature and pressure ranges (T = 220–3000 K; P = 1 × 10−4–100 bar). The calculated results show that the HO2 radical can attack C2H5 via a barrierless addition mechanism to form the energy-rich intermediate IM1 C2H5OOH (68.7 kcal/mol) on the singlet PES. The collisional stabilization intermediate IM1 is the predominant product of the reaction at high pressures and low temperatures, while the bimolecular product P1 C2H5O + OH becomes the primary product at lower pressures or higher temperatures. At the experimentally measured temperature 293 K and in the whole pressure range, the reaction yields P1 as major product, which is in good agreement with experiment results, and the branching ratios are predicted to change from 0.96 at 1 × 10−4 bar to 0.66 at 100 bar. Moreover, the direct H-abstraction product P16 C2H6 + 3O2 on the triplet PES is the secondary feasible product with a yield of 0.04 at the collisional limit of 293 K. The present results will be useful to gain deeper insight into the understanding of the kinetics of the C2H5 + HO2 reaction under atmospheric and practical combustion conditions.
Highlights
With low molecular weight, small polarity, and high volatility, alkanes can enter the atmosphere and are one of the main components of urban atmospheric pollutants
The geometries of all of the reactants, products, intermediates, and transition states involved in Methods the C2 H5 + HO2 reaction were optimized at the second-order Møller-Plesset perturbation MP2 [13]
2H5 + HO2 reaction are shown in Figure 1a,b along with the available experimental data from the the literature
Summary
Small polarity, and high volatility, alkanes can enter the atmosphere and are one of the main components of urban atmospheric pollutants. They are mainly released into the atmosphere through abstraction, distillation, refining, and combustion of fossil fuel, as well as combustion and natural decomposition of organics. R· is the initial product of pyrolysis, oxidization, combustion, or a photochemical reaction of saturated hydrocarbons. It can make a quick addition reaction with O2 , an important step to generate an alkane peroxy radical (RO2 ·). Considering the actual application values of R· in combustion, atmospheric chemistry, and biological process [1,2,3,4,5,6,7,8], many experimental and theoretical research
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