Unimolecular Dissociation of Gaseous Ions in EI Mass Spectrometry.

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  • TAKEUCHI Takae
    Department of Chemistry, Faculty of Science, Nara Women's University

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  • ＥＩマススペクトルにおける気相イオンからの単分子分解反応の研究
  • EI マススペクトル ニ オケル キソウ イオン カラ ノ タンブンシ ブンカ

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The fragmentation mechanisms of gaseous ions were studied experimentally and theoretically. In order to contribute to construction of fragmentation theory in mass spectra, the principle was examined using three separate approaches. Firstly, energy dependence on the fragmentation of molecular ions was investigated using the threshold electron-photoion coincidence (TEPICO) technique. Secondary, fragmentation mechanisms of molecular ions (n-butane, 1-propanol, n-propyl amine, and cycloglycylglycine cation radicals and a series of organosilicon cation radicals) in the low energy region were studied using ab initio molecular orbital (MO) methods. Finally, the dissociation (by hydrogen loss) of the first excited state (Ã2B1) of the formaldehyde cation as a function of its vibrational excitation was analyzed. Its mechanism involved an electronic predissociation by the ground X2B2 state in the tunneling regime. A statistical treatment for nonadiabatic interactions accounted for the low value of the rate constant as well as for a large isotope effect that persists over an energy interval of ca. 0.7 eV.

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