Prediction of the energy dependence of molecular fragmentation cross sections for collisions of swift protons with ethane and acetylene

We report the energy-dependent fragmentation cross sections for several of the more likely fragmentation channels for protons with up to 10 keV impact energy colliding with acetylene and ethane. We find that the predominant channels are those which involve the dissociation of a carbon-hydrogen bond, and we find that the cross sections for these channels are maximum in the low-projectile-energy region. The cross sections for fragmentation involving dissociation of a C-C bond are an order of magnitude smaller and peak at somewhat higher projectile energy. Although there are no experimental values with which to compare, it appears that selection of projectile energy can be used to influence branching ratios in proton-hydrocarbon collisions and, by implication, in other ion-molecule and atom-molecule collisions.