Mechanistic and kinetic study of the OH+C2H5CN reaction

The OH-initiated atmospheric reaction mechanism and kinetics for levoglucosan emitted in biomass burning

Levoglucosan is a typical molecular tracer of biomass-burning aerosols in the atmosphere. The mechanism for OH-initiated reaction with levoglucosan is studied at the level of MPWB1K/6-311+G(3df,2p)//MPWB1K/6-31+G(d,p). The possible subsequent reactions in the presence of O2, NO and H2O are also taken into consideration. The study shows that the H atom abstraction from the C4-position by the OH radical is an energetically favorable pathway, and that the OH-initiated products contribute to the formation of SOA and atmospheric acidity. The kinetic calculation is performed and the rate constants are calculated over the temperature range of 200-1500 K, using the Rice-Ramsperger-Kassel-Marcus (RRKM) theory. The rate constant of levoglucosan reacting with the OH radical at 298 K is 2.21×10(-13) cm(3) molecule(-1) s(-1) and the atmospheric lifetime is 26 days ([OH]=2.0×10(6) molecule cm(-3)). The equilibrium constants both in gas phase and aqueous are computed. The free energy ΔG indicates that, the subsequent reactions tend to take place more spontaneously once the reaction occurs. This work provides a comprehensive investigation about OH-initiated atmospheric reactions with levoglucosan, which is helpful for experiment and risk assessment.

Mechanistic and kinetic study on the ozonolysis of n-butyl vinyl ether, i-butyl vinyl ether and t-butyl vinyl ether

Density functional theory (DFT) and ab initio method are employed to elucidate the mechanisms for O(3)-initiated oxidation of n-butyl vinyl ether (n-BVE) and its isomers (i-BVE and t-BVE). For each BVE, the reactions proceed via O(3) cycloaddition resulting in the formation of primary ozonides (POZs) and then two self-decomposition pathways of POZs are followed. Major products are identified to be formaldehyde and butyl formates (CH(3)CH(2)CH(2)CH(2)OCHO for n-BVE, (CH(3))(2)CHCH(2)OCHO for i-BVE and (CH(3))(3)COCHO for t-BVE). The total and individual rate constants for main product channels have been calculated using the modified multichannel Rice-Ramsperger-Kassel-Marcus (RRKM) approach. At 298 K and 101 kPa, the calculated total rate constants are 2.50×10(-16), 3.41×10(-16) and 4.17×10(-16) cm(3) molecule(-1) s(-1) for n-BVE+O(3), i-BVE+O(3) and t-BVE+O(3), respectively, which are in perfect agreement with experimental results. The total rate coefficients are almost pressure independent in the range of 0.001-101 kPa but obviously positive temperature dependent over the whole study temperature range (200-400 K). Also, the favorable reaction pathways have been determined through the estimation of branching ratios. Moreover, the influence of alkoxy group structure on the reactivity of vinyl ethers was examined.