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

Abstract

An experimental procedure is reported, which provides the absolute triple differential cross sections (ATDCSs) for electron-impact ionization of large (bio)molecules. This type of measurements represents the most stringent tests for new or existing theoretical models. We will use this procedure to test the accuracy of the best currently available theoretical models for the problems of electron-impact (65 eV) ionization of the molecules water $({\mathrm{H}}_{2}\mathrm{O})$, tetrahydrofuran $({\mathrm{C}}_{4}{\mathrm{H}}_{8}\mathrm{O})$, and their hydrogen-bonded dimer ${\mathrm{H}}_{2}\mathrm{O}\ifmmode\cdot\else\textperiodcentered\fi{}{\mathrm{C}}_{4}{\mathrm{H}}_{8}\mathrm{O}$. The cross sections were calculated using the 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 which cover almost the full solid angle of the ejected electron and a broad range of ejected electron energies and projectile scattering angles, 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. These theoretical models, however, become less adequate for the ATDCS of ${\mathrm{C}}_{4}{\mathrm{H}}_{8}\mathrm{O}$, 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.