Thesis. 1977. Sc.D.--Massachusetts Institute of Technology. Dept. of Physics. / Microfiche copy available in Archives and Science. / Bibliography : leaves 221-223. / by Riad Ahmad Bitar. / Sc.D.

Lam Chow Shing. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references. / Abstracts in English and Chinese. / Thesis Examination Committee --- p.i / Abstract --- p.ii / Acknowledgements --- p.iv / Table of Contents --- p.v / List of Tables --- p.vii / List of Figures --- p.viii / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- The Gaussian-3 Method --- p.1 / Chapter 1.2 --- The G3 Method with Reduced MΦller- Plesset Order and Basis Set --- p.2 / Chapter 1.3 --- Density Functional Theory (DFT) --- p.3 / Chapter 1.4 --- Calculation of Thermodynamical Data --- p.3 / Chapter 1.5 --- Remark on the Location of Transition Structures --- p.3 / Chapter 1.6 --- Natural Bond Orbital (NBO) Analysis --- p.4 / Chapter 1.7 --- Scope of the Thesis --- p.4 / Chapter 1.8 --- References --- p.5 / Chapter Chapter 2 --- Theoretical Study of Tri-s-triazine and Its Derivatives --- p.7 / Chapter 2.1 --- Introduction --- p.7 / Chapter 2.2 --- Methods of Calculation --- p.9 / Chapter 2.3 --- Results and Discussion --- p.9 / Chapter 2.3.1. --- Property of Tri-s-triazine --- p.9 / Chapter 2.3.2. --- Substituent Effects on the Properties of the Tri-s-triazine Parent Molecule --- p.10 / Chapter 2.3.3. --- Heats of Formation of Derivatives of Tri-s-triazine --- p.20 / Chapter 2.4 --- Conclusion --- p.22 / Chapter 2.5 --- References --- p.22 / Chapter Chapter 3 --- A Gaussian-3 Study of the Dissociative Photoionization of Acetone --- p.25 / Chapter 3.1 --- Introduction --- p.25 / Chapter 3.2 --- Methods of Calculation --- p.26 / Chapter 3.3 --- Results and Discussion --- p.26 / Chapter 3.3.1. --- "Formation of m/z = 42 (CH2CO+.),43 (CH3CO+) Ions" --- p.31 / Chapter 3.3.2. --- Formation of m/z = 43 (c-CH2CHO+) and m/z = 15 (CH3+) Ions --- p.32 / Chapter 3.3.3. --- Formation of m/z = 57 (CH3COCH2+) Ions --- p.37 / Chapter 3.3.4. --- Formation of m/z = 39 (C3H3+) Ions --- p.38 / Chapter 3.4 --- Conclusion --- p.40 / Chapter 3.5 --- Publication Note --- p.40 / Chapter 3.6 --- References --- p.40 / Chapter Chapter 4 --- "A G3(MP2) Study of the C3H60+. Isomers Fragmented from l,4-Dioxane+" --- p.42 / Chapter 4.1 --- Introduction --- p.42 / Chapter 4.2 --- Methods of Calculation --- p.43 / Chapter 4.3 --- Results and Discussion --- p.44 / Chapter 4.3.1. --- "Formation of C3H60+. Isomers 1 and 2 via Fragmentation of 1,4-Dioxane+" --- p.44 / Chapter 4.3.2. --- Reaction with Acetonitrile --- p.55 / Chapter 4.3.3. --- Reaction with Formaldehyde --- p.57 / Chapter 4.3.4. --- Reaction with Ethylene --- p.61 / Chapter 4.3.5. --- Reaction with Propene --- p.63 / Chapter 4.4 --- Conclusion --- p.67 / Chapter 4.5 --- Publication Note --- p.68 / Chapter 4.6 --- References --- p.68 / Chapter Chapter 5 --- A Computational Study of the Photodissociation Channels of Chloroiodomethane --- p.71 / Chapter 5.1 --- Introduction --- p.71 / Chapter 5.2 --- Methods of Calculation --- p.73 / Chapter 5.3 --- Results and Discussion --- p.74 / Chapter 5.3.1 --- CH2C1 + I(2P1/2) and CH2C1 + I(2P3/2) Channels --- p.77 / Chapter 5.3.2 --- "CH2I + C1(2P3/2,1/2) Channel" --- p.78 / Chapter 5.3.3 --- CHI + HC1 Channel --- p.80 / Chapter 5.3.4 --- CH2 + IC1 Channel --- p.81 / Chapter 5.4 --- Conclusion --- p.82 / Chapter 5.5 --- Publication Note --- p.83 / Chapter 5.6 --- References --- p.83 / Chapter Chapter 6 --- Conclusion --- p.86 / Appendix A --- p.87 / Appendix B --- p.89

Fullerenes have highly excited electronic states with interesting properties for possible wide ranging applications including in electronics. These highly excited, Rydberg-like states, so-called superatom molecular orbitals (SAMOs), are diffuse low-angular momenta states with molecular orbitals centred on the hollow fullerene core. The SAMOs can be detected by femtosecond photoelectron spectroscopy (PES) and characterised by photoelectron angular distributions (PADs) combined with time-dependent density functional theory (TD-DFT) calculations. The photoelectron spectra of C60 and C70 show a peak structure below kinetic energies corresponding to the photon energy, superimposed on a thermal electron background. This peak structure was assigned to one-photon ionisation of the SAMO states based on PAD and TD-DFT. In this thesis, studies of the fullerene species C82 and Sc3N@C80 revealed PES and PAD with similar features to C60 and C70. The SAMO peaks became less prominent compared to the thermal electron background for increasing molecular size and decreasing symmetry, and were almost absent for the endohedral species. To provide more information about the influence of encapsulated atoms in the fullerene cage on the SAMO states, experiments on Li@C60 have been carried out. A lower thermal electron emission temperature and a splitting of the SAMO peaks has been observed for Li@C60 compared to C60. Nevertheless the binding energies are remarkably similar in all investigated fullerenes, which is important for any applications. Since the binding energies are about the same, but the ionisation potentials of the fullerenes are different, the excitation energy to the SAMOs scales with the ionisation energy. The reasons for the well-pronounced peak structure of the SAMO states in the PES of C60 could be explained by the similarity of the SAMOs to Rydberg states along with the higher photoionisation probabilities compared to valence states which were modelled by Benoît Mignolet and Françoise Remacle. As the SAMOs are highly excited electronic states, like Rydberg states, the potential energy surface of the neutral molecule and the ionised molecule are similar. Therefore the vibrational energy is conserved in the molecule during the photoionisation on the femtosecond time scale. The TD-DFT calculations on C60, carried out by Benoît Mignolet and Françoise Remacle, revealed the photoionisation probabilities of the SAMOs to be at least three orders of magnitude higher than for non-SAMOs for the applied experimental conditions. To test the prediction of the model, the relative photoionisation probabilities of the s-SAMO to p-SAMO and the s-SAMO to d-SAMO were obtained experimentally from the PES at various photon energies (2-3.5 eV) within this work. The analysis indicates remarkable agreement between the experiment and the theoretical values. Further quantum chemical calculations on a series of polycyclic aromatic hydrocarbons (PAHs) were carried out within this thesis, which revealed similar Rydberg-like molecular orbitals in analogy to the SAMOs in fullerenes. The first series included benzene, naphthalene, anthracene, tetracene, pentacene and hexacene. The second series consisted of phenanthrene, pyrene and coronene. Finally, the third series covered cubane, adamantane and dodecahedral C20. All modelled molecules showed diffuse, excited electronic states similar to the SAMOs. Within each series the binding energies of these states decrease with increasing molecular size as well as the ionisation energies, except for the 3rd series. A comparison between all series shows that the binding energies of the states for the 3rd series (the 3-D series) are slightly higher than for the 1st and 2nd series in relation to similar molecular size. The results of the coronene calculations are compared to experimental photoelectron spectra and are shown to be in good agreement with the experiments.

Wannierfunctions are a superposition of the Blochorbitals in a Brillouin zone belonging to a manifold of energy bands. These Wannier functions have several uses regarding the analysis of the crystal on a local level. Since the Bloch orbital has a gauge indeterminacy and the Wannier functions therefore is strongly non-unique, the natural choice is the maximally localized Wannier funcition. These can be calculated from the standard Bloch orbital using unitary transformation by a steepest descent algorithm as proposed by Nicola Marzari and David Vanderbilt. Here the argument for this algorithm is discussed and explained.

This dissertation explores the use of photoelectron imaging spectrometry to probe the molecular electronic structure of various chemical systems, with an emphasis on photoelectron angular distributions. Experimental ion generation, mass selection, laser photodetachment, and photoelectron ion imaging were all done in a photoelectron imaging spectrometer described in detail. Results from simplistic systems, OH- and CH-, are used to illustrate the general and fundamental capabilities of imaging spectroscopy and angular distributions. This illustration is then expanded when both qualitative and quantitative analyses of photoelectron angular distributions are used to aid in the understanding of the electronic structure of several heterocyclic aromatic systems. First a qualitative analysis aids in the exploration of the electronic structure of thiophenide, C₄H₃S⁻, and furanide, C₄H₃O⁻. Ground and excited C₄H₃S and C₄H₃O radical states are observed, and bond dissociation energies are defined. Next, a new model used to qualitatively analyze photoelectron angular distributions resulting from mixed s - p hybrid states is presented and applied to detachment from pyridinide, C₅H₄N⁻; as a benchmark system. Before further exploring this model, the synthesis of several deuterated heterocyclic compounds is presented in order to determine the experimentally produced systems in our experimental setup. The electronic structure of the resultant molecules oxazolide, C₃H₂NO⁻, and thiazolide, C₃H₂NS⁻; are then investigated. Using this new qualitative model, the mixed s - p states model, to evaluate the angular distributions of the systems, the hybridization of the anion molecular orbitals is probed. Comparison of the photoelectron angular distributions that are modeled for each heterocyclic aromatic system yields several trends relating aromatic stabilization, molecular hybridization, and bond dissociation energies. A new qualitative model is then presented to evaluate photoelectron angular distributions resulting from mixed p - d states and applied to detachment from NO⁻. Finally, new ideas and directions are proposed.

Visualizing atomic orbitals.

A mechanism for alkene metathesis has been proposed by Chauvin, wherein metal carbenes act as catalysts for the reaction. The use and discovery of Fischer-, Tebbe-, Grubbs- and Schrock-type metal carbenes have to a certain extent proven the general mechanism. These metal carbenes showed different activity for alkene metathesis. Only Grubbs- and Schrock-type carbenes proved to be highly active for metathesis. A lot of studies have been done on the reasons for the activity, but still the main factors are unknown. In this study a molecular modelling investigation into the mechanism of the alkene metathesis reaction is done in an attempt to identify a factor(s) that can predict activity. By defining and knowing factors that contribute to activity, new catalysts can be designed that are truly active and selective. Fischer-, Tebbe-, Grubbs- and Schrocktype metal carbenes are investigated in this regard. The results of the investigation indicate that the frontier molecular orbital theory shows a possibility for prediction of alkene metathesis activity. By observing the size and location of the atomic orbital coefficients of the molecular orbital, the site of primary overlap for formation of metathesis products could be identified. The largest atomic orbital coefficient of the LUMO should be located on the metal atom. An atomic orbital coefficient should also be present on the carbene carbon for secondary overlap for formation of the metallacyclobutane intermediate. By exchanging the ruthenium in the second generation Grubbs catalyst framework the effect of the metal could be elucidated. The results clearly showed the important influence the metal atom has on the electronic properties of the catalyst complex. The results of frontier molecular orbital calculations supported the general activity trend of the four main types of metal carbenes for the metathesis of linear alkenes. By changing the metal in known catalyst frameworks a deeper understanding can be gained for the design of new alkene metathesis catalysts. / Thesis (PhD (Chemistry))--North-West University, Potchefstroom Campus, 2013

A mechanism for alkene metathesis has been proposed by Chauvin, wherein metal carbenes act as catalysts for the reaction. The use and discovery of Fischer-, Tebbe-, Grubbs- and Schrock-type metal carbenes have to a certain extent proven the general mechanism. These metal carbenes showed different activity for alkene metathesis. Only Grubbs- and Schrock-type carbenes proved to be highly active for metathesis. A lot of studies have been done on the reasons for the activity, but still the main factors are unknown. In this study a molecular modelling investigation into the mechanism of the alkene metathesis reaction is done in an attempt to identify a factor(s) that can predict activity. By defining and knowing factors that contribute to activity, new catalysts can be designed that are truly active and selective. Fischer-, Tebbe-, Grubbs- and Schrocktype metal carbenes are investigated in this regard. The results of the investigation indicate that the frontier molecular orbital theory shows a possibility for prediction of alkene metathesis activity. By observing the size and location of the atomic orbital coefficients of the molecular orbital, the site of primary overlap for formation of metathesis products could be identified. The largest atomic orbital coefficient of the LUMO should be located on the metal atom. An atomic orbital coefficient should also be present on the carbene carbon for secondary overlap for formation of the metallacyclobutane intermediate. By exchanging the ruthenium in the second generation Grubbs catalyst framework the effect of the metal could be elucidated. The results clearly showed the important influence the metal atom has on the electronic properties of the catalyst complex. The results of frontier molecular orbital calculations supported the general activity trend of the four main types of metal carbenes for the metathesis of linear alkenes. By changing the metal in known catalyst frameworks a deeper understanding can be gained for the design of new alkene metathesis catalysts. / Thesis (PhD (Chemistry))--North-West University, Potchefstroom Campus, 2013

Spin-orbit coupling and the related effects of A-doubling and spin-splitting have been well known to spectroscopists for some considerable time. The importance of these phenomena stems from the advent of radioastronomy and the study of the interstellar medium. Identification of the molecules, and the molecular transitions, in the interstellar dust clouds is necessary for an understanding of the cooling process by which these clouds can contract to form new stars.

Thesis (Ph.D.) in Chemistry--University of Maine, 2008. / Includes vita. Includes bibliographical references (leaves 181-195).