A. The photodissociation of Oxalyl Chloride at 248 nm
The probable reaction pathways for photodissociation of Oxalyl Chloride at
248 nm have been investigated by ab initio electronic structure calculation. The optimized geometries for reactant, intermediate, transition states, and dissociation products on the adiabatic ground state potential energy surface are searched at the level of B3LYP/cc-pVTZ. The energies are refined by CCSD(T)/cc-pVTZ with B3LYP/cc-pVTZ zero-point energy corrections. The RRKM rate constants are utilized in obtaining the most probable paths and branching ratio of dissociation products. The major product is found to be p2 (COClCO) with branching ratio about 0.87, which is a good fit to experiment (0.9).
B. Reaction dynamics of Si (3P) + Dimethylacetylene (CH3CCCH3) reaction
In this thesis, we investigated the reaction of Si (3P) – C2H6 (X1A1g) in single
collision condition. Density functional theory with functional, B3LYP and coupled cluster theory, CCSD, with cc-pVTZ basis sets are used to optimize the geometries of the collision complexes, intermediates, products and transition states on both triplet and singlet surfaces. Their energies are further computed with CCSD/CBS with B3LYP/cc-pVTZ zero-point energy corrections. In this reaction, the triplet complexes can cross singlet surface via intersystem crossing. The minimum-energy crossing structures are predicted by MCSCF method with TZVPP basis set. The H2-loss products observed experimentally are presumably singlet due to lower energies. The RRKM rate constants are computed to estimate product yields on singlet surface. The major product is found to be p73, with a yield of 98%.

Abstract
Table of Contents………………………………………………………………..………I

A. The photodissociation of Oxalyl Chloride at 248 nm
1. Introduction……………………………….………………………………………1
2. Theoretical methods………………………………………………………………3
2.1 Ab initio electronic structure calculations for the reaction pathway…3
2.2 Coupled cluster singles, doubles, and triples CCSD(T)…………………3
2.3 RRKM rate constant calculations………………………………………4
3. Results and Discussions……………………………………………………………5
3.1 Reactant → Intermediate 1 (i1)……………………..……………………5
3.2 Intermediate 1 (i1) → Intermediate 2 (i2)………………………………5
3.3 Intermediate 1 (i1) → Product 1 ( 2CO + Cl2 )……………...……………6
3.4 Intermediate 2 (i2) → Product 2 + Cl……………………………………6
4. Conclusion…………………………………………………………………..………7
References……………...………………………………………………………………..9
Table I. Oxalyl Chloride energy with cc-pVTZ basis set…………………………...12
Table II. Oxalyl Chloride energy with cc-pVTZ+d basis set……………….………13
Table III. Oxalyl Chloride energy with aug-cc-pVTZ basis set…….……………...14
Table IV. The RRKM rate constant……………………………………….…………15
Figure I. The reaction path of Oxalyl Chloride…………………….………………16
Figure II. The optimized geometries of reactant, intermediates, and products for dissociation channels of Oxalyl Chloride………………….....……..……17
Figure III. The optimized geometries of transition states for dissociation channels of Oxalyl Chloride…………………………………………...……………19
Figure IV. The reaction mechanism of Oxalyl Chloride……..…………..…………20
B.　Reaction dynamics of Si (3P) + Dimethylacetylene (CH3CCCH3) reaction
1. Introduction……………………………….…………………………………….…21
2. Theoretical methods………………………………………………………………23
2.1 Ab initio electronic structure calculations for the reaction pathway…23
2.2 CPMCSCF(Coupled Perturbed Multi-Configuration Self-Consistent Field) ………………………………………..……………………………23
2.3 RRKM (Rice-Ramsperger-Kassel-Marcus theory)………………..…..24
2.4 Complete Basis Set(CBS)………………………..…………………….….24
3. Results and Discussions…………………………………………………………25
3.1 Collision Complexes……….…………………………...…………………25
3.2 Reaction and pathways…………………..……….………………………26
3.3 Dissociation product with H2-eliminated…………….….………………31
3.4 The most probable paths…………………………….….………………32
4. Conclusion…………………………………………………………………………33
References……………...………………………………………………………………35
Table I. Si + DMA energy with cc-pVTZ basis set………………...………………...39
Table II. The RRKM rate constant…………………………………………………..65
Table III. Relative dissociate yields of the reactant…………………………………76
Figure 1. The reaction pathway from c1…………………………………….……….77
Figure 2. The reaction pathway from i17………………………………..….……….78
Figure 3. The reaction pathway from i23…………………………………..….…….79
Figure 4. The reaction pathway from i1…………………………………….……….80
Figure 5. The reaction pathway from i6…………………………………….……….81
Figure 6. The reaction pathway from i4 group….………………………….……….82
Figure 7. The reaction pathway from i2’…………………………………….………83
Figure 8. The reaction pathway from i16………………………………….………...84
Figure 9. The reaction pathway from i58………………………………….……..….85
Figure 10. The reaction pathway from i54 group….……………………….……….86
Figure 11. The reaction pathway from i60……………………….………….……….87
Figure 12. The reaction pathway from i78………………………………….……….88
Figure 13. The reaction pathway from i79………………………………….……….89
Figure 14. The reaction pathway from i92………………………………….……….90
Figure 15. The reaction pathway from i44 group……….………………….……….91
Figure 16. The reaction pathway from triplet state………………..……….……….92
Figure 17. The probably pathway of Si + DMA……..………………………...…….93
Figure 18. The optimized geometries of reactant, complex c1 and intermediates...94
Figure 19. The optimized geometries of products………………………………….111
Figure 20. The optimized geometries of transition states………………………….118
Figure 21. The most probable reaction mechanism…...…………………...………138
Figure 22. The concentration evolution…………………………………………….140
Figure 23. The IRC pathways of each channel…………………………...………..144

A.
1. J. C. Farman, B. G. Gardiner, and J. D. Shanklin, “Large losses of total ozone in Antarctica reveal seasonal ClOx/NOx interaction.” Nature 315, 207 (1985).
2. M. J. Molina and F. S. Rowland, “Stratospheric sink for chlorofluoromethanes: chlorine atom-catalysed destruction of ozone.” Nature 249, 810 (1974).
3. (a) P. A. Newman, “Chapter 5: Stratospheric photochemistry section 4.2.8 Clx catalytic reactions.” (b) Todaro, Richard M., “Stratospheric ozone: an electronic textbook. NASA goddard space flight center atmospheric chemistry and dynamics branch.” (2007).
4. M.S. Zahniser and F. Kaufman, “Kinetics of the reaction Cl + O3 → ClO + O2.” Elsevier 37, 226 (1975).
5. M. Ahmed, D. Blunt, D. Chen, and A. G. Suits, “UV photodissociation of oxalyl chloride yields four fragments from one photon absorption.” J. Chem. Phys. 106, 7617 (1997).
6. B. Ghosh, D. K. Papanastasiou, and J. B. Burkholder, “ClC(O)C(O)Cl: UV/vis spectrum and Cl atom photolysis quantum yields at 193, 248, and 351 nm.” J. Chem. Phys. 137, 164315 (2012).
7. (a) A. D. Becke, “Density-functional thermochemistry. III. The role of exact exchange.” J. Chem. Phys. 98, 5648 (1993). (b) A. D. Becke, “Density‐functional thermochemistry. I. The effect of the exchange‐only gradient correction.” J. Chem. Phys. 96, 2155 (1992). (c) A. D. Becke, “Density‐functional thermochemistry. II. The effect of the Perdew–Wang generalized‐gradient correlation correction.” J. Chem. Phys. 97, 9173 (1992). (d) C. Lee, W. Yang, and R. G. Parr., “Development of the Colle-Salvetti correlation-energy formula into a functional of the electron density.” Phys. Rev. B 37, 785 (1988).
8. (a) G. D. Purvis III and R. J. Bartlett, “A full coupled‐cluster singles and doubles model: the inclusion of disconnected triples.” J. Chem. Phys. 76, 1910 (1982). (b) H. Claudia, A. P. Kirk, and W. Hans-J, “A comparison of the efficiency and accuracy of the quadratic configuration interaction (QCISD), coupled cluster (CCSD), and Brueckner coupled cluster (BCCD) methods.” Chem. Phys. Lett. 190, 1 (1992). (c) J. K. Peter, H. Claudia, and W. Hans-J, “Coupled cluster theory for high spin, open shell reference wave functions.” J. Chem. Phys. 99, 5219 (1993).
(d) M. J. O. Deegan and P. J. Knowles, “Perturbative corrections to account for triple excitations in closed and open shell coupled cluster theories.” Chem. Phys. Lett. 227, 321 (1994).
9. I. N. Levine, “Quantum chemistry.” p.567 (2004).
10. J. Čížek, “On the correlation problem in atomic and molecular systems. Calculation of wavefunction components in Ursell‐type expansion using quantum‐field theoretical methods.” J. Chem. Phys. 45, 4256 (1996).
11. J. Čížek and J. Paldus, “Coupled cluster approach.” Phys. Ser. 21, 251 (1980).
12. R. J. Bartlett, “Coupled-cluster approach to molecular structure and spectra: a step toward predictive quantum chemistry.” J. Phys. Chem. 93, 1697 (1989).
13. J. Paldus, J. Čížek, and B. Jeziorski, “Coupled cluster approach or quadratic configuration interaction?” J. Chem. Phys. 90, 4365 (1989).
14. J. A. Pople, M. H. Gordon, and K. Raghavachari, “Quadratic configuration interaction: reply to comment by Paldus, Cizek, and Jeziorski.” J. Chem. Phys. 90, 4635 (1989).
15. A. H. H. Chang, A. M. Mebel, X. Yang, S. H. Lin, and Y. T. Lee, “Ab initio/ RRKM approach toward the understanding of ethylene photodissociation.” J. Chem. Phys. 109, 2748 (1998).
16. R. A. Marcus, “Unimolecular dissociations and free radical recombination reactions.” J. Chem. Phys. 20, 359 (1952).

B.
1. I. Langmuir, “The arrangement of electrons in atoms and molecules” J. Am. Chem. Soc. 41, 868 (1919).
2. I. Langmuir, “Isomorphism, isosterism and covalence” J. Am. Chem. Soc. 41, 1543 (1919).
3. J. P. Kenny, W. D. Allen, and H. F. Schaefer III, “Complete basis set limit studies of conventional and R12 correlation methods: the silicon dicarbide (SiC2) barrier to linearity.” J. Chem. Phys. 118, 7353 (2003).
4. I. Fernández, M. Duvall, J. I-C. Wu, P. v. R. Schleyer, and G. Frenking, “Aromaticity in group 14 homologues of the cyclopropenylium cation.” Chem. Eur. J. 17, 2215 (2011).
5. P. S. Thomas, N. P. Bowling, N. J. Burrmann, and R. J. McMahon, “Dialkynyl carbene derivatives: generation and characterization of triplet tert-butylpentadiynylidene (t-Bu−C≡C−C̈−C≡C−H) and dimethylpentadiynylidene (Me−C≡C−C̈−C≡C−Me).’’ J. Org. Chem. 75, 6372 (2010).
6. R. A. Seburg, E. V. Patterson, and R. J. McMahon, “Structure of triplet propynylidene (HCCCH) as probed by IR, UV/vis, and EPR spectroscopy of isotopomers.” J. Am. Chem. Soc. 131, 9442 (2009).
7. Y. T. Lee, J. D. McDonald, P. R. LeBreton, and D. R. Herschbach, “Molecular beam reactive scattering apparatus with electron bombardment detector.” Rev. Sci. Instrum. 40, 1402 (1969).
8. G. Scoles, “Atomic and molecular beam methods” Oxford University Press:  New York (1988).
9. D Sillars, R. I. Kaiser, N. Galland, and Y. Hannachi, “Crossed-beam reaction of boron atoms, B (2Pj), with dimethylacetylene, CH3CCCH3 (X1A1g):  untangling the reaction dynamics to form the 1,2-dimethylene-3-bora-cyclopropane molecule.” J. Phys. Chem. A 107, 5149 (2003).
10. L. C. L. Huang, H. Y. Lee, A. M. Mebel, S. H. Lin, Y. T. Lee, and R. I. Kaiser, “A combined crossed beam and ab initio investigation on the reaction of carbon species with C4H6 isomers. II. The dimethylacetylene molecule, H3CCCCH3 (X1A1g).” J. Chem. Phys. 113, 9637 (2000).
11. R. I. Kaiser and A. M. Mebel, “The reactivity of ground state carbon atoms with unsaturated hydrocarbons in combustion flames and in the interstellar medium.” Int. Rev. Phys. Chem. 21, 307 (2002).
12. R. I. Kaiser, “Experimental investigation on the formation of carbon-bearing molecules in the interstellar medium via neutral-neutral reactions.” Chem. Rev. 102, 1309 (2002).
13. N. Balucani, O. Asvany, A. H. H. Chang, S. H. Lin, Y. T. Lee, R. I. Kaiser, H. F. Bettinger, P. v. R. Schleyer, and H. F. Schaefer III, “Crossed beam reaction of cyano radicals with hydrocarbon molecules. II. Chemical dynamics of 1-cyano-1-methylallene (CNCH3CCCH2; X1A′) formation from reaction of CN (X2Σ+) with dimethylacetylene CH3CCCH3 (X1A1′).” J. Chem. Phys. 111, 7472 (1999).
14. R. I. Kaiser and N. Balucani, “The formation of nitriles in hydrocarbon-rich atmospheres of planets and their satellites: laboratory investigations by the crossed molecular beam technique.” Acc. Chem. Res. 34, 699 (2001).
15. R. I. Kaiser, S. Maity, B. B. Dangi, Y. S. Su, B.J. Sun, and A. H. H. Chang, “A crossed molecular beam and ab initio investigation of the exclusive methyl loss pathway in the gas phase reaction of boron monoxide (BO; X2Σ+) with dimethylacetylene (CH3CCCH3; X1A1g).” Phys. Chem. Chem. Phys. 16, 989 (2014).
16. T. Yang, A. M. Thomas, B. B. Dangi, R. I. Kaiser, M. H. Wu, B. J. Sun, and A. H. H. Chang, “Formation of the 2,3-dimethyl-1-silacycloprop-2-enylidene molecule via the crossed beam reaction of the silylidyne radical (SiH; X2Π) with dimethylacetylene (CH3CCCH3; X1A1g).” J. Phys. Chem. A 120, 7262 (2016).
17. E. Herbst, “Chemistry in the interstellar medium.” Annu. Rev. Phys. Chem. 46, 27 (1995).
18. Johns Hopkins University, “Dark bands in starlight: new milky way maps help solve stubborn interstellar material mystery.” Science News August 14 (2014).
19. (a) A. D. Becke, “Density‐functional thermochemistry. I. The effect of the exchange‐only gradient correction.” J. Chem. Phys. 96, 2155 (1992). (b) A. D. Becke, “Density‐functional thermochemistry. II. The effect of the Perdew–Wang generalized‐gradient correlation correction.” J. Chem. Phys. 97, 9173 (1992). (c) A. D. Becke, “Density-functional thermochemistry. III. The role of exact exchange.” J. Chem. Phys. 98, 5648 (1993). (d) C. Lee, W. Yang, and R. G. Parr., “Development of the Colle-Salvetti correlation-energy formula into a functional of the electron density.” Phys. Rev. B 37, 785 (1988).
20. G. D. Purvis III and R. J. Bartlett, “A full coupled‐cluster singles and doubles model: The inclusion of disconnected triples.” J. Chem. Phys. 76, 1910 (1982).
21. Æ. Frisch, M. J. Frisch, F.R. Clemente, and G. W. Trucks, “GAUSSIAN 09, Revision B.01, Gaussian, Inc.” Wallingford, CT, (2010).
22. O. K. Rice and H. C. Ramsperger, “Theories of unimolecular gas reactions at low pressures.” J. Am. Chem. Soc. 49, 1617 (1927).
23. O. K. Rice and H. C. Ramsperger, “Theories of unimolecular gas reactions at low pressures II.” J. Am. Chem. Soc. 50, 617 (1928).
24. L. S. Kassel, “Studies in homogeneous gas reactions I.” J. Phys. Chem. 32, 225 (1928).
25. L. S. Kassel, “Studies in homogeneous gas reactions II.” J. Phys. Chem. 32, 1065 (1928).
26. R. A. Marcus, “Unimolecular dissociations and free radical recombination reactions.” J. Chem. Phys. 20, 359 (1952).
27. “A glossary of terms used in chemical kinetics, including reaction dynamics” IUPAC Recommendations, 185 (1996).
28. K. A. Peterson, D. E. Woon, and T. H. Dunning, “Benchmark calculations with correlated molecular wave functions. IV. The classical barrier height of the H+H2→H2+H reaction.” J. Chem. Phys. 100, 7410 (1994).