Quantum symmetry and photoreactivity of azabenzenes

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The fundamental processes associated with a photochemical reaction are described with reference to experimental properties of azabenzenes. Consideration of both excitation and relaxation processes led to presentation of the symmetry propagator, a unifying principle which maps system fluctuations (perturbations acting on an initial state) with dissipations (transitions to different states), thus directing the energy flow along competing reactive and nonreactive pathways. A coherent picture of relaxation processes including chemical reactions was constructed with the aid of spectroscopic data. Pyrazine (1,4 diazine) possesses vibronically active modes which provide an efficient mechanism for internal conversion to the first excited singlet state, where ... continued below

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199 p.

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Chesko, J. D. M. June 1995.

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The fundamental processes associated with a photochemical reaction are described with reference to experimental properties of azabenzenes. Consideration of both excitation and relaxation processes led to presentation of the symmetry propagator, a unifying principle which maps system fluctuations (perturbations acting on an initial state) with dissipations (transitions to different states), thus directing the energy flow along competing reactive and nonreactive pathways. A coherent picture of relaxation processes including chemical reactions was constructed with the aid of spectroscopic data. Pyrazine (1,4 diazine) possesses vibronically active modes which provide an efficient mechanism for internal conversion to the first excited singlet state, where other promoting modes of the correct symmetry induce both intersystem crossing to the triplet manifold, isomerization through diaza-benzvalene, and chemical reactions through cycloreversion of dewar pyrazine to yield HCN plus an azete. At higher energies simple H atom loss and internal conversion become more predominant, leading to ring opening followed by elimination of methylene nitrile and ground state reaction products. Efficiency of chemical transformations as dissipation mechanisms versus competing fluorescence, phosphorescence and radiationless relaxation was mapped from near ultraviolet to far ultraviolet by photodissociation quantum yields into reaction channels characterized by molecular beam photofragment translational spectroscopy. A reaction path model for azabenzene photochemistry was presented and tested against experiment. Presence of undiscovered channels in other azabenzene systems was predicted and verified. The dominant process, HCN elimination, was resolved into three distinct channels. Both molecular and atomic hydrogen elimination was observed, the former with significant vibrational excitation. Small yields of isomerization products, acetylene and N2, were also observed.

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199 p.

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OSTI as DE95014867

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  • Other Information: TH: Thesis (Ph.D.)

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  • Other: DE95014867
  • Report No.: LBL--37342
  • Grant Number: AC03-76SF00098
  • Office of Scientific & Technical Information Report Number: 95285
  • Archival Resource Key: ark:/67531/metadc794469

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Office of Scientific & Technical Information Technical Reports

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  • June 1995

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  • Dec. 19, 2015, 7:14 p.m.

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  • April 5, 2016, 12:04 p.m.

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Chesko, J. D. M. Quantum symmetry and photoreactivity of azabenzenes, thesis or dissertation, June 1995; California. (digital.library.unt.edu/ark:/67531/metadc794469/: accessed September 20, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.