ECAMP 15

Ionization of molecules by electron impact represents one of the most fundamental interactions in nature, whose interest is relevant to a wide range of applications. Kinematically complete (e,2e) experiments, in which the energies and momenta of all final-state particles are determined, provide the most detailed information on the ionization reaction through the triple differential cross-section (TDCS). Experimentally, performing such measurements is difficult also because
of the close spacing between electronic states, as well as to the contributions of rotational and vibrational states. Theoretically, finding an accurate quantal description of multicenter continuum states is a formidable task. All models available in the literature are based on perturbative treatments. Even by making a number of approximations, the computational cost of TDCS calculations is huge.

We have recently [1] put forward a theoretical approach, named M3CWZ, which allows to calculate molecular ionization TDCS in reasonable times. In this model exchange effects and post-collision interaction are taken into account, and the continuum electrons (incident, scattered, and ejected) are all described by a Coulomb wave that corresponds to distance-dependent charges generated from the molecular target properties. We have applied it to study, at low impact energies, the ionization of the 1b1 and 3a1 orbitals of water molecules in several geometrical and kinematical configurations, all in the dipole regime. The M3CWZ model is thoroughly tested with an extensive comparison with available theoretical results and COLTRIMS measurements performed at projectile energies of Ei = 81 eV [2] and Ei = 65 eV [3]. Similar to other theoretical models, an overall good agreement with both sets of measured data is observed for the angular distributions. Our calculated cross-sections’ magnitudes are also satisfactory when compared to the other theoretical results, as well as to the cross-normalized relative scale data at 81 eV impact energy. The 65 eV set of data, measured on an absolute scale, offers a further challenging task for theoretical descriptions, and globally the M3CWZ performs fairly well and comparably to other theories.

The proposed approach with variable charges somehow allows to capture the main multicenter distortion effects while avoiding high computational costs.

[1] Tamin et al, J. Chem. Phys. 161, 164305 (2024)
[2] Ren et al., Phys. Rev. A 95, 022701 (2017)
[3] Zhou et al., Phys. Rev. A 104, 012817 (2021)