Failure of Cross-Section Additivity for Electron Capture from Hydrocarbon Gases to Bound States of Hydrogen Ions

Abstract

The measured total electron-capture cross sections per number of carbon atoms in ${\mathrm{C}}_{m}{\mathrm{H}}_{n}$ ($m=1, 2, 3, 4$), $\frac{{\ensuremath{\sigma}}_{c}}{m}$, decrease with increasing $m$. This decrease is largest at the lowest velocities of 0.8-3 MeV $_{1}^{1}\mathrm{H}^{+}$ ions, and diminishes in the limit of high velocities where the strict additivity of atomic cross sections in a molecular target is approached. The breakdown of the additivity rule in the present data is primarily attributed to, and accounted for in terms of, intramolecular electron loss processes.