Electron capture inH++H2

Abstract

Electron capture in ${\mathrm{H}}^{+}$+${\mathrm{H}}_{2}$ collisions is studied at energies of 1.0, 2.0, and 3.0 keV in the reduced angular range $\ensuremath{\tau}\ensuremath{\le}3.0$ keV deg. Time-of-flight techniques are used for state identification, and the probability of electron capture to $\mathrm{H}(1s)+{\mathrm{H}}_{2}^{ +}(^{2}\ensuremath{\Sigma}_{g}^{+})$ in an exchange collision is determined. This is shown to be the dominant exchange channel at small scattering angles. The "summed" exchange channels have a reduced cross section that is found to peak in the forward direction and shows no structure, while the cross section for capture to final ground-state channels shows some small structure at 3.0 keV for $\ensuremath{\tau}\ensuremath{\ge}1.5$ keV deg. The reduced cross section, at 1.0 keV, for capture to excited states of H (with the ${\mathrm{H}}_{2}^{+}$ in its ground state) is found to have a maximum at $\ensuremath{\tau}=1$ keV deg. The results are in agreement with a previously proposed model for ion-molecule charge exchange.