Cross sections for ionization and ionic fragmentation of pyrimidine molecules by electron collisions

The electron impact mass spectroscopy and the total ion collection measurements were used to investigate the ionization and ionic fragmentation of the pyrimidine, C4H4N2, molecules in the gas phase. The cation mass spectra were measured in the 10−85 amu range and the observed mass peaks assigned to corresponding ionic fragments. The most abundant cation in the mass spectra is the parent cation, C4H4N \hbox{$_{\mathrm{2}}^{\mathrm{+}}$} + 2 , at 80 amu. The appearance energies of the ionic fragments were determined and the possible fragmentation processes are discussed. The electron impact absolute total and partial ionization cross sections in pyrimidine were obtained over the energy range from the respective ionization thresholds up to 150 eV.