Ion-atom excitation at high and intermediate energies

Exact post and prior impulse approximation cross sections are calculated for the excitation process H⁺+H (1s to n=2). The results show a large post-prior discrepancy and a huge disagreement with the experiments, even at energies where the simple Born approximation already works. Following a previous work along this line, the authors show that the theory remarkably improves when the correct asymptotic conditions are observed by including eikonal phases. This new approximation, called the eikonal impulse approximation, presents a negligible prior-post discrepancy at high energies and the prior version produces very good agreement with the experiments. Departure of the total excitation cross section from the quadratic law on the projectile charge (saturation) is discussed and compared with the available data. Scaling laws, alignment factors and s-p coherences are reported and compared with previous results.