Shafranyosh M. Processes of positive and negative ion production of cytosine, thymine and uracil molecules by electron impact

Dissertation work is devoted to studying the processes of positive and negative ion production of cytosine, thymine, uracil molecules in the gas phase under the influence of slow electrons. This work is carried out a crossed electron and molecular beam technique.The absolute values of the total cross sections of production of positive ions of nucleic acid bases: cytosine, thymine, uracil molecules and energy dependences of ionization cross-sections from a threshold to 200 eV incident electron energy range have been determined. The absolute values of the total cross sections of production of negative ions of these molecules from a threshold to 5 eV are determined. It is shown that the process of negative ion production has resonant character and is accompanied with dissociation of molecules. The mass spectra of cytosine, thymine, uracil molecules are investigated at the electron energy 95 eV. The most intensive lines of the mass spectra correspond to the molecular ions and also for the fragmentation products of the pyrimidine rings. The schemes of fragmentation of molecules are offered. The cross-sections and the energy dependences of the ionic fragment production (partial cross-sections) of the cytosine, thymine, uracil molecules are defined. It is shown that the largest ion formation cross-sections are characteristic for the molecular ions.7452