Classical description of water molecules in collisions with fast ions*

The study of fast ions impinging on molecules of biological interest has become a field of interest in recent years. This is due to a need of atomic data for inelastic processes, involving specifically the water molecule, for hadron therapy. Different theoretical methods, historically used for ion-atom collisions, are being adapted to deal with molecular targets, such as the Classical Trajectory Monte Carlo (CTMC) method, which is being applied for this task using multi-center potentials. However, the non-degeneracy of the molecular orbitals (MOs) and the electron interaction with a non-central potential imply some differences with respect to the atomic approach which need a deeper study. In this work, classical calculations, taking into account the alignment of the initial distribution for each MO, are compared to the quantum-mechanical Two-Center Basis Generator Method and to experimental data, in order to shed light on these issues.