Papp A. Mass-spectrometry of ionization and dissociative ionization processes of the amino acid molecules by electrons

Present work is dedicated to a complex experimental and theoretical investigation of the single and dissociative ionization of the amino acid molecules glycine, methionine, tryptophan and alanine under the slow (<100 eV) electron impact being accompanied by the fragmentation of the above molecule with subsequent analysis of the decay products. The physical processes of the low-energy (≤100 еV) electron interaction with the many-atom molecules have been described. The principal regularities of the analysis of the many-electron organic molecules mass-spectra at the electron impact have been considered. The experiments were carried out using a modified magnetic МИ-1201 mass-spectrometer. The mass-spectra of the above molecules have been measured together with the energy dependences of their ionization and dissociative ionization cross-sections. An experimental setup based on the magnetic МИ-1201 mass-spectrometer has been described. The main disadvantages of the conventional ion bean sources have been analyzed, the steps of their modification with the purpose to carry out the mass-spectrometric measurements for the gaseous species have been suggested. The absolute values of the appearance energies of the main ionic fragments of the molecules under study have been determined. In order to find the most probable mechanisms of their fragmentation due to the low-energy electron impact the bond lengths and orders of the neutral molecules have been analyzed using the above appearance energy values. The dynamics of the yield of the fragments having the same chemical composition has been compared for the case of the different amino acid molecules. It has been shown that the above molecules at fragmentation produce a series of neutral and ionized fragments of the same mass.