A Comparative Experimental and Theoretical Study on Doubly Differential Electron-Impact Ionization Cross Sections of Pyrimidine

To provide a comprehensive data set for track structure-based simulations of radiation damage in DNA, doubly differential electron-impact ionization cross sections of pyrimidine, a building block of the nucleobases cytosine and thymine, were measured for primary electron energies between 30 eV and 1 keV as a function of emission angle and secondary electron energy. The measurements were performed for secondary electron energies from 4 eV to about half of the primary electron energy and for emission angles between 25{\deg} and 135{\deg}. Based on the experimental doubly differential ionization cross sections, singly differential and total ionization cross sections of pyrimidine were determined and compared to calculations using the BEB model. In addition to the measurements, a theoretical approach for calculating triply and doubly differential ionization cross section was developed, which is based on the distorted wave Born approximation, a single center expansion of molecular orbitals and an averaging of the T-matrix over different molecular orientations. The calculated doubly differential ionization cross sections of pyrimidine show a qualitatively good agreement with the experimental results.