| Recently, the studies on the radical reactions related to combustion chemistry continue to attract the extensive attention. Particularly, the reactions of the oxygen and the unsaturated radical which the free electron is on the double-bond are focused. There are so many characters of these radicals, and the most important one is that they can form some very steady conjugate systems with oxygen, which can make the initialized isomers more steady and make the reaction easier to continue. In these radicals, C3H5 is attended as their especial stability and the rapid rate in the reactions. Because the system is so large, there are few persons who had calculated its detailed potential energy surface. In this article, the theoretical investigations on the mechanisms for C3H5+O2 reaction is carried out based on the quantum chemical calculating methods. For gaining the whole mechanisms of C3H5 +O2, we compare this system with some others such as the system of C2H3. The following is the main results:At first, we study the entrance of the reaction, and only one attacking modes are found:allyl attacks the O atom in the O2. this attack is regarded as a process without energy barriers by our calculations and the article about the ethylene. Single electron at the O atom and free electron at the allyl are likely formed covalent bond, and produced a initialized isomer m1 whose energy is 68.93kCal/mol lower that the reactants. From abover, we can deduce that the most suitable entrance step is that allyl attacks O atom in the O2 and forms isomer m1. So, in following chapters, we will mainly discuss the path from beginning of isomer m1. 2. Starting from m1, we can gain three products which can produce in thermodynamics(their energies is lower than the reactants), and work out their produce channels which connect with reactants. The followings are these four path:Path1(I): R(CH3CH=C*H+NO)(m1(trans-CH3CH=CHNO)(m6(cis- CH3CH=CHNO)(P1(C-H and C-O bonds in the six-member ring rupture and form CH3CCH +O2H)Path1(II): R(CH3CH=C*H+NO)(m1(trans-CH3CH=CHNO)(m6(cis- CH3CH=CHNO)(m9(H at the 2-C in allyl thansfers N site by 1,3-Oshift)(P1(C-O bond ruptures and form CH3CCH +O2H).Path2(I): R(CH3CH=C*H+O2)(m1(trans-CH3CH=CHOO)(m2(form COO three-member ring)(m3(C-C bond ruptures,at the same time forms C-O bond,then forms CH3CH-O-CHO) (P2(C-O bond ruptures and form CH3CHO+CHO)。Path2(II): R(CH3CH=C*H+O2)(m1(trans-CH3CH=CHOO)(m6(cis- CH3CH=CHOO)(m7(forms CCOO four-member ring by a diene addition reaction process)(m8(O-O bond in the four-member ring ruptures and forms CH3CH(O)CHO)(P2(C-C bond ruptures and form CH3CHO+CHO)。Path3(1):R(CH3CH=C*H+O2)(m1(trans-CH3CH=CHOO)(m2(form COO three-member ring)(m10(H connects C at COO three –member ring site transfers C site ) (m11(O-O bond in the three-member ring ruptures)(P3(C-C bond ruptures and form CH3CH2+CO2)。 Path3(1I):R(CH3CH=C*H+O2)(m1(trans-CH3CH=CHOO)(m2(form COO three-member ring)(m4(C-C bond ruptures and forms C-O bond at he same time ,then forms CH3CH-O-CHO)(m5(H connets C at CHO site transfer C site and form CH3CH2OCO)( P3(O-C bond ruptures and form CH3CH2+CO2)。Above the paths, There is only one transation TSm2m10 with high energy in Path3(1),so we can think that it might have some competitive produces at higher temperature, but the produces must be few. The energies of the other pathes are relatively low, so there are the feasible pathes in this system. Especiallly, The energies of the whole Path2(I) are relatively low and the course is simple, so it is the most feasible path in this system. 3.compared with C2H3+O2The path is similar to the main produce channel of C2H3. The only defference between these two system is that the step of m1( TSm1m2 is rate determinate step in system of C2H3, but it is m2(TSm2m3 in system of C3H5 as well as energies of transation and intermediates in system of C3H5 are lower than these in system of C2H3. We analy...
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