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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 (H2O), tetrahydrofuran (C4H8O), and
their hydrogen-bonded dimer H2O center dot C4H8O. 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 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.
