Dissociation of $\mathrm{H}_2^{}{}_{}{}^{+}$ Ions in Collision with H Atoms: 3 to 115 keV

The cross section for the production of fast protons in collisions between $\mathrm{H}_2^{}{}_{}{}^{+}$ ions and H atoms has been measured in the energy range 3 to 115 keV. The cross section for the same process with ${\mathrm{H}}_2$ as the target particle was also measured and results were compared with previous work as a test of the calibration method. The results show that the H-atom target is more effective in dissociating $\mathrm{H}_2^{}{}_{}{}^{+}$ than is the larger ${\mathrm{H}}_2$ molecule in the energy range 10 to 42 keV. This order of effectiveness is reversed below 10 keV and above 42 keV. Comparison of the H-target results with theoretical calculations based on the Born approximation shows that the collisional excitation of the lowest excited state of the $\mathrm{H}_2^{}{}_{}{}^{+}$ ion—the $2p{\sigma }_u$ state—contributes a minor fraction of the total fast-proton production at 115 keV and a major fraction at 3 keV. The differential angular distributions of the fast protons were found to be the same for the H and ${\mathrm{H}}_2$ targets at 10 keV.