Theoretical Investigations On The Reaction Mechanisms Of Several Typical Radicals Systems In Atmosphere And Combustion Chemistry

Recently, the studies on the radical reactions related to combustionchemistry and atmosphere chemistry have been attracting the extensiveattention of some scholars and scientists. Particularly, the experimentalcharacterization and theoretical description of the major products of thereaction and the reaction mechanisms are important topics. The theoreticalinvestigations on the reaction mechanisms of several important radicalreactions related to atmosphere chemistry and combustion chemistry weresystematically carried out. With the computational method, we can not onlyobtain the structures and energies of the intermediate isomers and transitionstates, but also establish a detailed potential energy surface, by means of whichwe can discuss possible reaction channels and reaction mechanisms, and thuspredict the possible major products. Some rules about this kind of radicalreactions have been summarized. The present results can provide theoreticalbasis for understanding the reaction processes and reaction mechanisms ofradical reactions related to atmosphere chemistry and combustion chemistryand for the future experimental measurements. The main results aresummarized as follows.1. The doublet and quartet potential energy surfaces (PES) of reactionC2H+O2 were calculated at the CCSD(T)/6-311G(d,p)//B3LYP/6-311G(d,p)level of the theory. The doublet PES shows 9 isomers, 15 transition states, 5products and 8 pathways, and the quartet PES displays 2 isomers, 2 transitionstates, 1 product and 4 pathways. After analysing the two kinds of PESs, twocompetitive pathways can be found on the doublet PES as follows: Path RP1(1): R(C2H+O2)→1→TS1-2→2 →TS2-6→6→TS6-P1 →P1(HCO+CO) Path RP2(4): R→1→TS1-P2→Complex1→P2 (HCCO+O) In pathway RP1(1), the relative energy of transition state TS1-2 is -212.22kJ.mol-1, however, in pathway RP2(4), the relative energy of transition stateTS1-Complex1 is -216.73 kJ.mol-1, and pathway RP2(4) has compared with thoseof pathway RP1(1). Therefore, we think that pathway RP2(4) is morepreferable to RP1(1), i.e., product P2 is the main product, and product P1 isminor. In addition, it is also possible that a little of products P3 and P5 areobtained. 2. The singlet and triplet potential energy surfaces (PES) of reaction HO2+ NO2 were systematically studied at the CCSD(T)/6-311G(d,p)//B3LYP/6-311G(d,p) level of the theory. The singlet PES showing 6 products,5 isomers, 16 transition states and 10 pathways is preferable to the triplet onefor this reaction. After analysing the pathways of the reaction, two competitivepathways on the singlet PES can be summarized as follows: Path RP1 (1):R(HO2+NO2)→TSR-P1 (OOHNO2)→P1(HNO2+O2) Path RP2 (4):R →TS1R-1 →1 →TS1-P2→P2 (trans-HONO+O2) Considering the conversion barrier heights and the relative energies of thetransition states involved in the two pathways, we think that Path RP2 (4) isthe major pathway of the reaction and Path RP1 (1) is minor pathway. ProductP2 (HCNO+O2) is the main product, and product P1 (HNO2+O2) is minor. Inaddition, it is also possible that a little of product P6 (NO3+OH) is obtained. 3. The doublet and quartet potential energy surfaces (PES) of reactionHO2+C2H2 were investigated at theCCSD(T)/6-311G(d,p)//B3LYP/6-311G(d,p)level. The doublet PES exhibiting 10 products, 16 isomers, 26 transition statesand 10 pathways is preferable to the quartet one for the reaction. Fourcompetitive pathways on the doublet PES can be summarized as follows:Path RP1 (1):R(HO2+ C2H2)→1→2→3→4→5→P1(CH2O+HCO) Path RP2 (2):R→1→2→3→4→5→6→7→P2(CO2+CH3) Path RP3 (3):R→1→2→3→4→5→6→P3(CO+CH3O) Path RP7 (6):R→1→2→P7(C2H3O+O) Path RP1(1) is the major pathway and Path RP2(2) is the minor one.Path RP2(2) is preferable to Path RP3(3), and Path RP3(3) is preferable toPath RP7(6). 4. The singlet and triplet potential energy surfaces (PES) of reactionHO2+C2H were calculated at the CCSD(T)/6-311G(d,p)//B3LYP/6-311G(d,p)level of the theory. The singlet PES represents 5 products, 9 isomers, 14transition states and 8 pathways. The triplet PES represents 2 products, 5isomers, 7 transition states and 2 pathways. After analyzing the two kinds ofPESs, two competitive pathways can be summarized as follows: Path RP1 (1):R(HO2+C2H)→1→3→4→P1(CO+H2CO) (singlet) Path RP7 :R(HO2+C2H)→3TSR-1→31→3TS1-P7→P7(HCCO+OH) (triplet) Path RP7 on the triplet PES is the major pathway of the reaction andPath RP1 (1) on the singlet PES is minor pathway. P7 (HCCO+OH) is themain product and P1 (CO+H2CO) is the minor. 5. The singlet and triplet potential energy surfaces (PES) of CS+O2reaction were calculated at the CCSD(T)/6-311G(d,p)//B3LYP/6-311G(d,p)level of the theory. The singlet PES shows 2 products, 3 isomers and 4transition states, and the triplet PES exhibits 1 product, 1 isomer and 2transition states. After analyzing the two kinds of PESs, two competitivepathways can be summarized as follows: Path RP1 (1):R(CS + O2)→TSR-1→1→TS1-2→2→TS2-3→3→TS3-P1 →P1(CO+SO) (singlet) Path RP3(6):R(CS + O2)→3TSR-1→31→3TS1-P3→P3(OCS+O) (triplet) Pathway RP3(6) on the triplet PES is the major pathway of the reaction...