A. Theoretical study of the Elusive N-hydroxyoxaziridine (c-H2CON(OH))
In this thesis, electronic structure calculations support the formation of N-hydroxyoxaziridine (c-H2CON(OH))–a structure strained three-membered ring via reaction of triplet carbene (3CH2) and singlet nitrous acid (1HONO). The geometries of complexes, intermediates, transition states, and products were optimized by CCSD/cc-pVTZ calculations, the minimal-energy crossing points (MSX) on the crossing surface of singlet and triplet states was obtained by CPMCSCF/TZVPP. The energies were calculated by CCSD(T)/CBS with CCSD/cc-pVTZ zero-point energy corrections. Likewise, MRCI/CBS are also used to assess the multi-reference effects. The results are compared with experiments in which vacuum ultraviolet (VUV) photoionization (PI), mass resolved in a reflectron time-of-flight mass spectrometer (PI-ReTOF-MS) to detect the compound were carried out.
B. Ionization potentials of C2H4O2 isomers
Ionization potential of C2H4O2 isomers were calculated, including acid, methylformate, glycolaldehyde, and ethene-diols. The structures of C2H4O2 isomers were optimized by B3LYP/cc-pVTZ calculations. The ionization potential and energies were computed by CCSD(T)/CBS with B3LYP/cc-pVTZ zero-point energy corrections. The ionization potential of C2H4O2 isomers were found in the range between 8.17eV and 10.84eV.

A. Theoretical study of the Elusive N-hydroxyoxaziridine (c-H2CON(OH)) 1
1. Introduction 1
2. Theoretical methods 5
2.1 Ab initio electronic structure calculations for the reaction pathway predictions 5
2.2 Hybrid functional B3LYP 5
2.3 Coupled cluster CCSD(T) 6
2.4 Reaction conical intersection 6
2.5 CCSD(T)/CBS calculations 6
2.6 MRCI/CBS calculations 7
3. Result and Discussions 9
a. Collision complexes 9
b. Intersystem crossing 11
c. Isomerization 12
d. The comparison inversion and rotation of complex c2, c2', c2'', and c2''' 13
e. The reaction pathway of 3c2 15
f. The reaction pathway of 1c2 17
g. The reaction pathway of the others 19
h. Effect of MRCI/CBS in this calculations 23
i. Comparison with the experimental results 24
4. Conclusion 27
5. Reference 29
Table 1. The configuration state functions generated by MCSCF(8,8) and MRCI(8,8) at cc-pVDZ, cc-pVTZ, and cc-pVQZ basis set, respectively. 32
Table 2 . The CCSD(T)/cc-pVDZ energies on the CCSD/cc-pVTZ optimized geometries of relevant reactants, complexes, transition states, products, and minimal-energy crossing points (MSX) on their adiabatic singlet or triplet ground state potential energy surfaces 38
Table 3. The calculated ionization potentials for the B3LYP/cc-pVTZ optimized geometries of CH3NO2 isomers and CCSD/cc-pVTZ//MRCI/CBS energies on the adiabatic singlet ground state potential energy surface. 47
Table 4. The CCSD(T)/cc-pVDZ and CCSD/cc-pVTZ//MRCI/CBS energies on the CCSD/cc-pVTZ optimized geometries of relevant reactants, complexes, transition states, minimal-energy crossing points (MSX) on their adiabatic singlet or triplet ground state potential energy surfaces of Figure 3. 58
Table 5. The CCSD(T)/cc-pVDZ and CCSD/cc-pVTZ//MRCI/CBS energies on the CCSD/cc-pVTZ optimized geometries of complexes and transition states on their adiabatic singlet or triplet ground state potential energy surfaces of Figure 7. 62
Table 6. The CCSD(T)/cc-pVDZ energies on the CCSD/cc-pVTZ optimized geometries of relevant reactants, transition states, and products on their adiabatic triplet ground state potential energy surfaces of Figure 5. 64
Table 7. The CCSD(T)/cc-pVDZ energies and CCSD/cc-pVTZ//MRCI/CBS energies on the CCSD/cc-pVTZ optimized geometries of relevant reactants, transition states, and products on their adiabatic singlet ground state potential energy surfaces of Figure 6. 66
Table 8. The ranges of isomers can be ionized at the lowest VUV energy. 69
Figure 1. The probable pathways of the CH2(3B1) + HONO(1A), in which the energy in kJ/mol relative to CH2(3B1) + HONO(1A),are compute with CCSD(T)/CBS at CCSD/cc-pvtz optimized geometries. 72
Figure 2. The probable pathways of the CH2(1A1) + HONO(1A), in which the energy in kJ/mol relative to CH2(3B1) + HONO(1A),are compute with CCSD(T)/CBS at CCSD/cc-pvtz optimized geometries. 73
Figure 3. The reaction pathways of singlet and triplet carbene (CH2) with nitrous acid (HONO). Energies are given in kJmol-1 with respect to the separated reactants on the triplet surface. The minimal-energy crossing points (MSX) are shown for inter system crossing (ISC) pathway as waved arrows. 74
Figure 4. Intrinsic reaction coordinate (IRC) calculations at the CCSD/cc-pVTZ//CCSD (T)/CBS level of theory, for the formation of complexes c1, c2, and c3 via addition of singlet carbene (CH2) to nitrous acid (HONO). 75
Figure 5. Decomposition pathways of triplet N-hydroxyoxaziridine (c-H2CON(OH); c2) 77
Figure 6. Decomposition pathways of singlet N-hydroxyoxaziridine (c-H2CON(OH); c2) 78
Figure 7. Isomerization processes of N-hydroxyoxaziridine (1c2). 79
Figure 8 . The CCSD/cc-pVTZ optimized geometries of transition states, in which the point group is in parenthesis, lengths in picometer, and the angles in degree. 80
Figure 9 . The CCSD/cc-pVTZ optimized geometries of reactants, complexes, and minimum-energy crossing points (MSX), in which the point group is in parenthesis, lengths in picometer, and the angles in degree. 84
Figure 10 . The CCSD/cc-pVTZ optimized geometries of intermediates, in which the point group is in parenthesis, lengths in picometer, and the angles in degree. 86
Figure 11 . The CCSD/cc-pVTZ optimized geometries of products, in which the point group is in parenthesis, lengths in picometer, and the angles in degree. 92
Figure 12. Structure of CH3NO2 isomers along with their ionization energies (IE) and relative energies (∆E) calculated at the B3LYP//CCSD(T)/CBS level of theory. 95
Figure 13. The IRC paths of each channel. 110
B. Ionization potentials of C2H4O2 isomers 131
1. Introduction 131
2. Theoretical methods 133
2.1 Ab initio electronic structure calculations for the ionization potentials 133
2.2 Hybrid functional B3LYP 133
2.3 CCSD(T)/CBS calculations 133
3. Result and Discussions 135
4. Conclusion 139
5. Reference 141
Table 1 . The calculated ionization potentials for the B3LYP/cc-pVTZ optimized geometries of C2H4O2 isomers. 144
Table 2. Molecule orbital of HOMO(16) diagram and electron density distribution 148
Acetic acid' 148
Methylformate 148
Glycolaldehyde'' 149
Glycolaldehyde''' 149
Ethene,1-1-diol 150
(E)-ethene,1-2-diol' 151
(E)-ethene,1-2-diol'' 151
Figure 1. The B3LYP/cc-pVTZ optimized geometries of C2H4O2 isomers and relative cations, lengths in angstrom, and the angles in degree. 152

A. Theoretical study of the Elusive N-hydroxyoxaziridine (c-H2CON(OH))
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