Excitation of helium by proton impact

Calculation of state-resolved excitation cross sections for proton-helium collisions has remained a challenge for many decades. Despite a significant amount of experimental work for some transitions, theory has only been available across limited energy ranges and with inconsistent accuracy. Furthermore, most measurements cover intermediate and high energies, but the data that is available for low energy collisions suggests that the cross sections can be significant in this region.

We have developed a semi-classical version of the Laguerre-based convergent close-coupling (CCC) approach to calculate a comprehensive dataset for excitation cross sections up to n<=5 in proton collisions with ground-state helium. Using a relatively large basis of 2586 target states we obtain convergence in both the state-resolved excitation and electron loss cross sections. The present results agree very well with experiment where available and provide significant improvement over previous calculations. Furthermore, our calculations accurately reproduce the Rosenthal oscillations seen in the experimental data, indicating a high level of accuracy in modelling the underlying physics.