Hybrid Quantum Mechanical - Quasi-Classical Model for Evaluating Ionization and Stripping Cross Sections in Atom-Ion Collisions

Ion-atom ionization cross sections are needed in many applications employing the propagation of fast ions through matter. When experimental data or full-scale theoretical calculations are non-existent, approximate methods must be used. The most robust and easy-to-use approximations include the Born approximation of quantum mechanics and the quasi-classical approach utilizing classical mechanics together with the Bohr-Sommerfeld quantization rule. A hybrid method has been developed for calculation of the ionization and stripping cross sections of ions or atoms by fast ions by combining the Born approximation of quantum mechanics and the quasi-classical approach in the regions of impact parameters in which they are valid, and summing the results to obtain the total cross section. The results of the modified approach agree better with the experimental data than either the Born approximation or the quasi-classical approach, applied separately. A new scaling formula for the ionization and stripping cross section of atoms and ions by fully stripped projectiles has been also proposed. The scaling has no fitting parameters and has been checked against 11 different pairs of projectile and target atoms. All of the experimental data overlap on a single curve in the proposed scaled coordinates.