Electron Transfer in Proton-Hydrogen-Atom Collisions: 2-117 keV

The cross section for electron transfer between a proton and a hydrogen atom has been measured in the energy range 2 to 117 keV. The apparatus employs a heated target chamber in which hydrogen gas is 79% dissociated. The total density of H atoms in the collision chamber, including both free H atoms and H atoms combined into ${\mathrm{H}}_2$ molecules, is determined by a differential-Coulomb-scattering measurement, while the density of ${\mathrm{H}}_2$ molecules is determined by a double-electron-capture measurement. Experimental values of the cross section measured at 19 different energies varied monotonically from 13.3×${10}^{-16\mathrm{}}$ ${\mathrm{cm}}^2$ at 1.92 keV to 0.064×${10}^{-16\mathrm{}}$ ${\mathrm{cm}}^2$ at 117.5 keV. The results, believed to be accurate to ±5%, are not completely consistent with previous measured values of other investigators. Theoretical calculations of McCarroll and McElroy agree satisfactorily with the measurements at energies lower than 60 keV, but between 60 and 117 keV no theoretical calculation is in satisfactory agreement with the measurements.