The description of molecular ionisation processes by electron impact represents a challenging scenario in the field of atomic collisions, given their relevance in both astrophysical and biological contexts. In particular, water (H₂O) and tetrahydrofuran (C₄H₈O or THF) have been considered biological system prototypes in radiation processes; hence, fully differential cross-sections have been recently measured for the electron impact single ionisation of these molecules [1, 2]. From a theoretical point of view, perturbative models have been the reasonable choice to analyse these processes, since the inherent complexity of these targets makes difficult the implementation of numerical intensive methods.
In this work we calculate and analyse fully differential cross-sections of the electron impact single ionisation of H₂O and THF by means of two single-centre approximations to the final state of the collisional process, which are variants of the perturbative method CDW-EIS. The first one approximates the molecular ion as a single centre of charge +1, while the second one spherically averages the anisotropic interaction with the residual ion. We benchmark our results with recent experimental data reported in the literature, where we observe good overall agreement for the impact energies considered [3]. In addition, we discuss different difficulties that arise by modelling multi-centre targets with single-centre wave functions.

[1] J. Zhou, E. Ali, M. Gong, S. Jia, Y. Li, Y. Wang, Z. Zhang, X. Xue, D. V. Fursa, I. Bray, X. Chen, D. Madison, A. Dorn, and X. Ren, Phys. Rev. A 104, 012817 (2021).
[2] X. Xue, D. M. Mootheril, E. Ali, M. Gong, S. Jia, J. Zhou, E. Wang, J.-X. Li, X. Chen, D. Madison, A. Dorn, and X. Ren, Phys. Rev. A 106, 042803 (2022).
[3] E. Acebal and S. Otranto, Phys. Rev. A 109, 062807 (2024).