| Reactions of ions and radicals play an important role in various fields, such as combustion processes, interstellar medium and planetary atmospheres. In this thesis, the potential energy surfaces of the ion/radical-molecule reactions of relevance to combustion chemistry, interstellar chemistry and planetary atmosphere chemistry have been expolored using quantum chemical methods. Important information such as geometries and energies of the reactant, isomers, transition states and products are obtained. Possible reaction channels as well as reaction mechanism are also provided. The results obtained in this thesis are compared with previous experimental findings and may shed some light on future experimental investigations of these kinds of reactions. The main results are summaried as follows:1. The potential energy surfaces for HCN+ reactions with CH4, C2H2, C2H4 and NH3are explored. The results are as follows:(1) Theoretical investigations on the doublet potential energy surface for the reaction of HCN+ with CH4 are carried out, the main reaction channels are listed as:Path 1: RHCN++CH4→HCNH…CH3+l→P1(HCNH++CH3)Path 2: R HCN++CH4→HCNH…CH3+ 1→HNCHCH3+ 2→P2(CH3CNH++H)Path 3: R HCN++CH4→HCNH…CH3+ l→HCNHCH3+3→H2CNCH3+4→CH3NC(…H)H+ 6→P3(HCNCH3++H)→P4(CH3++HCN+H)Path 4: R HCN++CH4→NC(H)…HCH3+ 8→NC(H)CH4+ 9→P5 (cNCHCH2++H2)Path 5: R HCN++CH4→HCNH…CH3+ 1→HNCHCH3+ 2→HNCHCH3+ 7→P6(NCCH3++H2)→P7(HCCNH++H2+H)P1(HCNH++CH3) is the most feasible product. P2(CH3CNH++H) and P3 (HCNCH3++H) are the second and third competitive products. Moreover, P3 (HCNCH3++H) and P6(NCCH3++H2) can undergo further evolutions leading to P4 (CH3++HCN+H) and P7(HCCNH++H2+H), respectively. However, both of them are theomodynamically unfeasible. (2)Theoretical calculations on the potential energy of the HCN++C2H2 reaction areperformed, main reaction pathways are as follows:Path 1: RHCN++C2H2→-HCCHCHN+ 1→NCCHCH2+ 4→Pi(H2C3N++H)Path 2: R HCN++C2H2→p-HCCHCHN+ 1→NCCHCH2+ 4→P2 (CN+C2H3+)Path 3: R HCN++C2H2→p-HCCHCHN+ 1→NCCHCH2+ 4→NCCCH3+ 6→P3(HC3N++H2)Path 4: R HCN++C2H2→HCNCHCH+ 3b→HCNCCH2+ 14→P7(C2H2++HCN)P1(H2C3N++H) is the most favorable product, P7(C2H2++HCN) and P3(HC3N++H2) may be the second and third feasible products, followed by the least possible product P2(CN+C2H3+).(3)For HCN++C2H4 reaction, main reaction pathways are shown as:Path 1: RHCN++C2H4→HCNCH2CH2+ 1→P1(HCN+C2H4+)Path 2: R HCN++C2H4→HCNCH2CH2+ 1→P2(HCNCHCH2++H)Path 3: R HCN++C2H4→HCNCH2CH2+ 1→NCCH2CH3+ 5→P3(NCCH2+CH3+)Path 4: R HCN++C2H4→N-cCHCH2CH2+ 3→c-CHCH2CH2N+ 4→CNCH2CH3+ 12→P4(CN+C2H5+)Path 5: R HCN++C2H4→HCNCH2CH2+ 1→NCCH2CH3+ 5→P5(NCCHCH2++H2)Path 6: R HCN++C2H4→N-cCHCH2CH2+ 3→c-CHCH2CH2N+ 4→c-NHCH2CH2C+ 8→HNCCH2CH2+ 9→P6(HNCCHCH2++H)P1(HCN+C2H4+) and P2(HCNCHCH2++H) are the major and minor product, respectively. Other products which may compete each other, are much less competitive.(4)For HCN++NH3 reaction, main pathways are as follows:Path 1: RHCN++NH3→HCNNH3+ 1→HCN…NH3+ 3→P1(NH3++HCN)Path 2: R HCN++NH3→NCHNH3+ 2→HNCHNH2+ 12→HNC…HNH2+ 13→P3(NH3++HNC)Path 3: R HCN++NH3→NCHNH3+ 2→HNCHNH2+ 12→HNC…HNH2+ 13→P9(HCNH++NH2)Path 4: R HCN++NH3→NCHNH3+ 2→HNCHNH2+ 12→P12(HNCNH<sup>2++NH2)Path 1 is the most competitive pathway. Path 2 and path 3 may compete each other.Path 4 may be the least possible pathway.3. A detailed theoretical study for the reactions of C(3P) with C3H6 and trans-C4H8 was investigated at G3B3//B3LYP/6-311G(d,p) level, the main results are as follows:(1) For C(3P)+C3H6 reaction, possible reaction pathways are as follows:Path 1: R C(3P)+C3H6→CH3-cCHCCH2 l→fra/w-CH3CHCCH2 2a→CH3C(…H)CCH2 3→P4(CH3CCCH2+H)Path 2: R C(3P)+C3H6→CH3-cCHCCH2 1→CH3CHCCH2(2a,2b)→P5(CH3CHCCH+H)Path 3: R C(3P)+C3H6→CH3-cCHCCH2 l→trans-CH3CHCCH2 2aPath 4: R C(3P)+C3H6→CH3-cCHCCH2 1→trans-CH3CHCCH2 2a→cis-CH3CHCCH22b→P7(CH2CCH+CH3)Path 1, 2 and 4 are the main pathways, they may compete each other. Path 3 is the minor pathway.(2)For C(3P)+ trans-C4H8 reaction, two feasible reaction pathways are obtained:Path 1: R C(3P)+ trans-C4H8→CH3-cCHCCH-CH3 l→cis-trans-CH3CHCCHCH3 3a→CH3CHCC(CH3)…H6→P6(CH3CHCCCH3+H)Path 2: R C(3P)+trans-C4H8→CH3-cCHCCH-CH3 1→cis-trans-CH3CHCCHCH3 3a→P7(CH3CHCCH+CH3)Path 1 and path 2 may compete each other, both of which are the main channels. 3. A detailed mechanistic study was reported for the reactions of CH with C3H6 and CH3CCH, the results are as follows:(1)For CH+C3H6 reaction, main reaction pathways are listed as:Path 1: R CH+C3H6→CH3-cCHCHCH21 (a, b)→P1(CH3-cCHCHCH+H)Path 2: R CH+C3H6→CH3-cCHCHCH21 (a, b)→P2(CH3-cCCHCH2+H)Path 3: R CH+C3H6→CH3-cCHCHCH21 (a, b)→P3(cCHCHCH2+CH3)Path 4: R CH+C3H6→CH-CH3CHCH2 2→CH2CH2CHCH2 4(a,b)→P4(cis-CH2CHCHCH2+H)Path 5: R CH+C3H6→CH…CH3CHCH2 2→CH2CH2CHCH2 4 (a, b)→P5(trans-CH2CHCHCH2+H)Path 4 and 5 may compete each other, they are the most possible pathways. Paths 1, 2 and 3 may have comparable contributions to the title reaction.(2)For CH+CH3CCH reaction, main reaction pathways are as follows:Path 1: R CH+CH3CCH→CH3CCHCH 1a→CH3-cCCHCH 2→P3(CH3-cCCCH+H) Path 2: R CH+CH3CCH→CH3CCHCH 1a→CH3CHCCH 3→P5(CH2CHCCH+H)Path 3: R CH+CH3CCH→CH3CCHCH la→CH3CCCH2 4→P6(CH2CCCH2+H)Path 4: R CH+CH3CCH→CH3CCHCH 1a→CH2CHCHCH 5 (a, b, c, d)→P7(C2H2+C2H3)Path 1, 2 and 3 are the major reaction channels, they may compete each other. Path 4 is the minor reaction channel.
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