Absolute triple differential cross sections for low-energy electron impact ionization of biochemically relevant systems: Water, tetrahydrofuran, and hydrated tetrahydrofuran

Ionizing interactions between charged particles and biochemically relevant systems have attracted considerable interest owing to their important roles in many fields, e.g. medical radiation therapy. Here, an experimental procedure for the absolute triple differential cross sections (ATDCS) of electron-impact ionization (65 eV) of large biomolecules: water (H₂O), tetrahydrofuran (C₄H₈O), and their hydrogen-bonded dimer H₂O·C₄H₈O is reported. The absolute scale of the cross section is determined using He as a reference gas, whose absolute cross sections can be obtained reliably. The experimental data were measured using a reaction microscope, which can cover nearly the entire 4π solid angle for the secondary electron emission over a range of ejection energies. The experimental data are compared to the theoretical calculations with the currently available molecular three-body distorted-wave (M3DW) model, the multicenter three-distorted-wave (MCTDW) approach, and the multicenter three-distorted-wave using the Ward-Macek approximation (MCTDW-WM). When compared to the new experimental ATDCS results, it is found that the data for water are generally well reproduced by the M3DW model, while strong deviations in the absolute magnitude of the cross sections are found for the MCTDW. The MCTDW-WM model provides improved agreement over the MCTDW due to the inclusion of post-collision interaction (PCI) effect. These theoretical models, however, become less adequate for the ATDCS of C₄H₈O, in particular concerning the absolute magnitude. Furthermore, we find that a water environment can play a noticeable role for the ionization dynamics in the case of hydrated molecules.