Theoretical Investigations On The Mechanisms For The Reactions Of N_mO_n(m,n=1,2) Molecules With Several Important Radicals

NmOn(m,n=1,2) compounds have received much attention because oftheir toxic effects as atmospheric pollutants generated from the combustion offossil fuels. To repress them, studies on the reactions of NmOn with a series ofsmall radicals, as an important part of atmospheric and combustion chemistries,have continued to attract experimental and theoretical chemists. As a result,quantum chemical investigations on the potential energy surfaces for thereactions of NmOn with several important radicals have been carried out in thisthesis. The reactions include C2＋NO,3C2＋NO2,NCO＋NO2,NCS＋NO2, 3C2H＋NO2 ,HCCN ＋NO,C2N＋NO and CN＋N2O. The importantinformation of potential energy surfaces such as the structures and energies ofintermediate isomers and transition states, possible reaction channels, reactionmechanisms and major products can be obtained from the theoreticalinvestigations. Some conclusions in the present thesis may be helpful for thefurther theoretical and experimental studies of this kind of reactions. The mainresults are summarized as follows. 1. For a deeper understanding of the mechanism of C2+NO reaction in 3combustion environments, both doublet and quartet potential energy surfaces(PES) of the reaction have been worked out at the CCSD(T)/6-311G(d)//B3LYP/6-311G(d) level of theory. There are 6 isomers, 9 transition states, 4products and 11 pathways on the doublet PES. There are 4 isomers, 7transition states, 3 products and 3 pathways on the quartet PES. Afterconsidering the two kinds of PESs, four competitive pathways can be found onthe doublet PES: Path RP1(1): R C2+NO →1 CCNO→2 (NC)CO→3 CNCO → P1 CN+CO 3 Path RP1(2): R → 1 → 4 CC(NO) → 2 → 3 → P1 CN+CO Path RP2(1): R → 1 → P2 O+2CCN 3 Path RP3(1): R → 1 → 5 ON(CC) → P3 O+2CCNring 3At lower temperatures(T < 968 K), pathways RP1(1) and RP1(2) are the majorpathways and product P1 CN+CO is the major product. On the other hand,pathways RP2(1) and RP3(1) possess more competitive abilities at highertemperatures(T > 3000 K) and products P2 O+2CCN and/or P3 O+2CCNring 3 3are the major products. 2. The doublet and quartet potential energy surfaces (PES), with thedoublet one being more preferable, were calculated at the G2(B3LYP/MP2/CC)//B3LYP/6-311G(d) level of theory in order to make clear the possibleassociation and dissociation mechanisms of C2+NO2 reaction. There are 4 3isomers, 9 transition states, 4 products and 5 pathways on the doublet PES.After considering the doublet PES, four competitive pathways can be found: Path RP1(1): R C2+NO2 → 1 CCN(O)O → 2 OCCNO → P1 CO+CNO 3 Path RP2(1): R → 1 → 2 → 3 OC(O)CN → P2 CO2+CN Path RP3(1): R → 1 → 2 → 3 OC(O)CN → P3 CO+NCO Path RP3(2): R → 1 → 2 → 4 OCC(O)N → P3 CO+NCOPathway RP1(1) is more preferable to pathway RP2(1), pathway RP2(1) ismore preferable to pathway RP3(1), and pathway RP3(1) is more preferable topathway RP3(2). 3. The singlet and triplet potential energy surfaces (PES) were consideredat the Gaussian-3//MP2/6-311G(d) level of theory to elucidate the mechanismof NCO＋NO2 reaction. The singlet PES involving 4 isomers, 4 transitionstates, 2 products and 2 pathways is more preferable to the triplet one for thisreaction. The two pathways on the singlet PES can be summarized as follows: Path RP1(1): R NCO+NO2 → 1 O(O)NNCO → 2 ON(NC(O)O) → P1NNO+CO2 Path RP2(1): R→ 3 cis-trans-ONONCO → 4 cis-cis-ONONCO→ P2CO+2NOPathway RP1(1) is the major pathway and pathway RP2(1) is the minor onefor NCO＋NO2 reaction. 4. The singlet and triplet potential energy surfaces (PES) were consideredat the HL//MP2/6-311G(d) level o...