The Dissociation of Fast H$_2^+$ Ions by Hydrogen

H$_2^+$ ions of energy 100 to 800 keV have been passed through hydrogen gas and the cross-sections for the following four processes determined: \begin{equation*}\tag{1}H_2^+ \rightarrow H^+ + H^0,\end{equation*} \begin{equation*}\tag{2}H_2^+ \rightarrow H^+ + H^+,\end{equation*} \begin{equation*}\tag{3}H_2^+ \rightarrow H^0 + H^0,\end{equation*} \begin{equation*}\tag{4}H_2^+ \rightarrow H_2^0.\end{equation*} A magnetic field was used to separate the fast dissociation products of different e/m, and CsI(Tl) scintillation crystals were used as detectors. Double-height pulses resulted when two particles of the same e/m simultaneously entered one of the crystals and were clearly resolved from single pulses. Processes (3) and (4) were separated by moving a fine slit across the neutral-particle counter which thus counted only H$_2^0$ particles as double pulses. The partial cross-sections for processes (1) and (2) show an E$^{-1}$ dependence at high energies. The energy dependence is less marked below 300 keV, where the Born approximation might be expected to be invalid. The partial cross-sections for processes (3) and (4) show the strong energy dependence characteristic of an electron-exchange process. The angular distribution for process (3) is consistent with the reaction proceeding via the 1$^3\sum_u$ repulsive triplet state. The large fraction of the capture reactions proceeding this way (70%), is reasonable considering the high probability of formation in the triplet state. The large values of the cross-sections for processes other than simple dissociation account, in part, for the considerable discrepancies between the results of other workers.