Methyl Ethyl Ketone And Methyl Isopropyl Ketone Multiphoton Ionization Dissociation Study

Multiphoton ionization dissociation refers to absorb several photons coherently and thus reach the ionization potential, which is an ionization method of molecules. As molecules are combined by atoms'chemical bonds, so the process of ionization is accompanied by chemical bonds fractured and molecules broken into molecular pieces.By absorbting a number of multiphotons, molecules are excited to some intermediate vibrated excited state (intermediate resonance state), which is easier to be Rydberg states and this process is called multiphoton resonance enhanced multiphoton ionization process (REMPI). Mass Spectrometry (MS) is an effective method of multiphoton ionization and dissociation. Through the laser interaction with organic compouds, the transition rate is greatly increased by absorbing several photons. Combined with time of flight mass spectrometry, fragment ions from the mass spectrum is analysed to study the cleavage channel and thus provide a certain amount of theoretical data for organic research and development. This paper mainly studies ketone molecules in multiphoton ionization dissociation. Ketone organic matter is an important organic matter, whose physical and chemical properties have diversity, and always be hot study on its photophysical and photochemical aspect. In recent years, such a simple molecule of acetone has been studied more.Acetone is always used as methyl and acetyl donor. Because of its simple structure and good symmetry, has been a hot research ketones. MEK is a common organic solvent widely used in industry, textile, chemical synthesis industry. In many respects, it can replace the highly toxic benzene. Methyl isopropyl ketone is an organic intermediates with a more bullish market, and primarily used as a synthetic activity of cationic dyes-1,3,3-Trimethyl Indole Lynn intermediates. The current domestic demand is very large and mainly is bases on import. This paper mainly studies the multiphoton ionization dissociation processes of methyl ethyl ketone and methyl isopropyl ketone at the 532nm laser-induced, combined with reflection time of flight mass spectrometry to study dissociation channels of the fragment ions. We also use Hatree-Fork method to optimize the geometries on the ground state and excited state about methyl ethyl ketone, methyl isopropyl ketone and calculate the energy. While use QST2 method to find its transition state, the conformational changes are explained in the dissociation reaction process.This paper is divided into five chapters. The first chapter is mainly about instruction, concludes a summary of multiphoton ionization dissociation, the definition and classification and characteristics of the principle of TOF-MS, Gaussian03 research methodology and theoretical basis. The second chapter is about experimental description on the instruments used in this paper and experimental procedure, experimental methods and theoretical methods. Chapter III analysis the multiphoton ionization dissociation process of the methyl ethyl ketone the 532 nm laser. By the time of flight mass spectrometry, we found that butanone frist absorbs two-photon to be dissociated and produced acetyl and ethyl, which is NorrishⅠ-type cleavage reaction. The MS signals are strong. At the same time we analysis fragments of C+,CH3+,C2H3O+ and C2H5+ about the relative intensity of these types of ions changes with the laser intensity changes, conclude that big fragment ions are increased with the laser intensity lenhanced, the small fragment ions are reduced with the laser intensity increases lowered. The fourth chapter studies the ionization dissociation process of methyl isopropyl ketone in the same experimental conditions. It believes that the main process of methyl isopropyl ketone molecules absorbs two photons to be dissociated into acetyl and isopropyl, and then absorbs two photons to be ionization state. The C2H3O+, CH3+, CO+are clearly visible from the MS diagram. Also we compare the change of fragments in different laser intensities and delay times. Chapter V is mainly theoretical analysis. We optimize the geometry and calculate energy on the level of HF /3-21G and the CIS/3-21G+about methyl ethyl ketone and methyl isopropyl ketone on the ground state and excited states, and find the carbonyl bond changes to a special bond that between carbon-oxygen single bond and double bonds. The transition state is also investigated by using QST2 method, while compared the variation of conformation with the ground state and excitated state. The results show that the bond broken process in concert with the variations of configuration is one-step process. While study that dissociation of CH3CO is not in tandem, but a one-step separated reaction.