Interaction of positronium with helium atoms - the classical treatment of the 5-body collision system

The interaction between positronium and a helium atom is studied using the 5-body classical trajectory Monte Carlo method. We present the total cross sections for the dominant channels, namely for single ionization of the target, and ionization of the projectile, resulting from pure ionization and also from electron transfer (capture or loss) processes for 1-5.7 a.u. incident velocities of the positronium atom. While the pure ionization channel is a one step, the ionization channel in combination with electron capture and loss is a two-step process. Eighteen different classical final states were distinguished. Our results were compared with the calculated data using hydrogen projectiles having the same velocities as well as with the experimental data in collisions between H and He [R.D. DuBois, A. Koever, Phys. Rev. A 40, 3605 (1989)]. We analyze the similarities and deviations for ionization of helium atoms by positronium and hydrogen projectile impact. We have shown that the projectile velocity dependent cross sections for the two major channels have very similar shapes. The agreement with the experimental results is excellent for the case of target single ionization and less satisfactory for projectile ionization. This is especially visible at high velocities. While for the case of target single ionization the absolute total cross sections are nearly the same for Ps or H projectiles for the case of projectile ionization the cross section is about two times higher for Ps than for H. This fact can be attributed to the difference between the binding energy of Ps and H