Balmer- alpha emission cross sections from collisions of He+ on H2, CH4, C2H2, C2H4, and C2H6: A study of Bragg additivity.

Abstract

Bragg additivity was explored through measurement of Balmer-\ensuremath{\alpha} emission cross sections produced by the collision of 100--350-keV ${\mathrm{He}}^{+}$ incident on ${\mathrm{H}}_{2}$, ${\mathrm{CH}}_{4}$, ${\mathrm{C}}_{2}$${\mathrm{H}}_{2}$, ${\mathrm{C}}_{2}$${\mathrm{H}}_{4}$, and ${\mathrm{C}}_{2}$${\mathrm{H}}_{6}$. The cross-section data show a linear relation on a Fano plot, thus indicating that the Bethe-Born theory may provide an appropriate description of the collision. Evidence for Bragg additivity would be a direct dependence of the value of the emission cross section on the number of hydrogen atoms in the target molecule. Results indicate a failure of strict additivity. Once molecular structure had been taken into account by a calculation of approximate electron densities, the cross sections followed an additive rule demonstrating a dependency not only on the number of hydrogens present, but also on the number of electrons available per hydrogen atom.