Electronically resolved excitation in proton collisions with H₂

When cosmic ray protons propagate through gas clouds in space they collide with atoms and molecules. In order to calculate the photon flux produced as a result of these collisions knowledge of the rovibrationally resolved cross sections for excitation is required. The most prevalent species in these environments is the hydrogen molecule, however, there are currently no measurements or calculations of state-resolved excitation cross sections in p⁺+H₂ collisions at keV energies. As a substitute, equivelocity scaling of the available data for electron collisions with H₂ is currently used to estimate the proton cross sections.

Using the semi-classical approach to ion collisions we have extended the molecular convergent close-coupling (MCCC) code to proton collisions with H₂. We have calculated fully converged fixed-nuclei excitation cross sections for transitions from the ground electronic state to H₂ states up to n=3 in the atomic limit. Comparison of the present results with the scaled electron cross sections reveals significant differences, suggesting that substitution of scaled electron data with ab initio cross sections for proton projectiles could improve the accuracy of modelling relying on this data.