Mechanistic And Kinetic Studies Of The Reactions Of Nitrils With Radicals

Nitril molecules (such as methyl cyanide, ethyl cyanide, acrylonitrile and propyl cyanide) are one of the most important class of oxygenated volatile organic compounds (VOCs). They are not only harmful for our health, but also contaminative for our environment. Thus it is especially important for nitril molecule to be translated and absorbed, in which the dominant absorption way is the reactions with radicals (e.g., OH, Cl, F).The reactions with radicals play an important role in the atmospheric environment, combustion and atmosphere of Titan. The mechanisms and kinetics of the reactions of nitril with radicals have been investigated deeply will play important roles in the aspect of environmental pollution.The mechanisms and kinetics of the reactions of nitril with radicals have been systematically studied employing quantum chemistry methods for the first time. The important and valuable results in this thesis are summarized as follows:1. The reaction of CH₃CN with C₂HA detailed theoretical study has been carried out on the mechanism and kinetics of the C₂H + CH₃CN reaction at the BMC-CCSD//BHandHLYP/6-311G(d, p) level. The results show that the reaction proceeds via five mechanisms: direct hydrogen abstraction, C-addition/elimination, N-addition/elimination, C₂H-to-CN substitution and H-migration mechanisms. The C-addition/elimination, N-addition/elimination and direct hydrogen abstraction channels are important thermodynamically and kinetically. Due to high barriers, the latter two mechanisms play secondary roles for the whole reaction. Conventional transition state model and multichannel RRKM theory were carried out the total and individual rate constants. The theoretical rate constants are in good agreement with experimental value. The rate constant calculations show that the overall rate constants have a positive temperature dependence and pressure independence. At lower temperatures, the C-addition step is the most favorable and the major products are CH₃ and HCCCN. However, at higher temperatures, the direct hydrogen abstraction channel, leading to C₂H₂ + CH₂CN is dominant.2.The reaction of C₂H₅CN with O(³P)We present an exhaustive and theoretical study on the reaction of C₂H₅CN with O(³P). The C₂H₅CN + O(³P) reaction can proceed via four kinds of mechanisms, i.e., methylene-H abstraction, methyl-H abstraction, C-addition/elimination and N-addition/elimination. The calculation results reveal that the methylene-H abstraction is the dominant channel over the whole temperature region. However, as the temperature increases, methyl-H abstraction becomes a strong competitive channel with methylene-H abstraction. Over the temperature range of 450-577 K, the calculated rate constants are in good agreement with available experimental values. The total rate constants for the title reaction are of strong positive temperature dependence. The calculated total and individual rate constants of the title reaction are fitted by a three-parameter formula over the temperature range of 200-2000 K and given in cm³ molecule^-1 s^-1 as follows: k = 5.18 x 10^-17 T ^2.10exp (-3739.76 / T) k₁ = 3.79 x 10^-17 T ^1.99exp (-3344.56 / T) k_2a= 1.73 x 10^-17 T ^2.07exp (-4188.78 / T) k_2b = 4.99 x 10^-17 T ^2.01exp (-4419.72 / T) k₃ = 3.26 x 10^-16 T ^1.54exp (-4537.11 / T)3. The reaction of C₂H₅CN with OHThe optimized geometries and harmonic frequencies of the reactants, products, local minima and transition states were obtained at the MP2/6-311G (d,p) level. To verify the reliability of MP2/6-311G(d,p) geometries, the optimizations of the key species were also performed at the BHandHLYP/6-311G(d,p) level. Single-point calculations were carried out using the G3(MP2) and BMC-CCSD methods. The hydrogen abstraction and addition/elimination channels are involved. Conventional transition state model and multichannel RRKM theory were carried out the total and individual rate constants. The results show thatα-H abstraction channel is important at lower temperatures, however, at higher temperatures, the C-addition/elimination channel becomes dominant and IM2 (C₂H₅C(O)NH) is the dominant product. The rate constant calculations show that the overall rate constants have positive temperature dependence. The calculated overall rate constant is in good agreement with the experimental value.