Fragmentation of molecular gases by 5-45 keV protons

Abstract

Collisions involving ionization and fragmentation by 5-45 kev protons during passage through thin targets of H₂, N₂, O₂, CO and CH₄ have been investigated by the mass spectroscopic analysis of the secondary ionic products of single collisions. Particular care was taken to ensure that all these ions were collected and recorded with high efficiency in spite of the wide spread in both their energies of formation and initial directions. Measured fragmentation cross sections are as much as five times larger than previously published values. It is shown that, although the energy variation of cross sections for the formation of undissociated molecular ions may be in general accord with the predictions of the simple adiabatic maximum rule, the application of this rule to dissociative processes involving the production of singly or doubly ionized fragments may give entirely misleading results. The measurements show that in all the cases investigated a significant fraction of the total secondary ion yield arises through collisions involving fragmentation.