Cusp formation in classical trajectory Monte-Carlo calculations of single atomic ionization by the impact of neutral projectiles

The Classical-trajectory Monte-Carlo (CTMC) model provides an excellent description of the electron capture to the continuum (ECC) cusp in atomic ionization collisions whenever the electron-projectile interaction is of a Coulomb or even of a dipolar type. However, in this communication we show that this description fails for the case of a polarizability potential, such as in the one produced by a neutral He (2(1)S) outgoing projectile. Actually the CTMC calculation predicts an ECC peak that is much broader and smaller than for a Coulomb interaction, a result that differs from experimental data and quantum-mechanical calculations.