Formation of positive and negative ions of thymine molecules under the action of slow electrons

The formation of positive and negative molecules of thymine–a base of nucleic acids–under the action of slow electrons is investigated by the method of crossed electron and molecular beams. The method developed makes it possible to measure the molecular beam intensity and determine the energy dependences and absolute values of total cross sections for the formation of positive and negative ions of thymine molecules. It is found that the maximal cross section for the formation of positive ions is reached at an energy of 95 eV and its absolute value is, accordingly, 1.4 $\times$ 10$^{-15}$ cm$^2$. The total cross section for the formation of negative ions is 8.2 $\times$ 10$^{-18}$ cm$^2$ at an energy of 1.1 eV. The mass spectra of thymine molecules are measured and the cross sections of dissociative ionization are determined.