Study of H2++He → HeH++H at low energies

Laboratory‐energy distributions of HeH⁺ were measured for the reaction ${\mathrm{H}}_2^{+}+\mathrm{He}\to {\mathrm{HeH}}^{+}+\mathrm{H}$ (endothermic by 0.81 eV for ground‐state reactants and products) with a merging‐beams apparatus over a range of interaction energy W from 0.05 to 12 eV. The He was in the ground state; the ${\mathrm{H}}_2^{+}$ was vibrationally excited. Absolute and relative cross sections were determined from these distributions. For $\text{W ≥ 5\hspace{0.17em}}\mathrm{eV}$ , the distributions show that in the center‐of‐mass system the HeH⁺ peaks along both the incident direction of the ${\mathrm{H}}_2^{+}$ and the incident direction of the He. The peak along the direction of the He is largest, and is the only one for W <5 eV. The role played by W and by the vibrational excitation of ${\mathrm{H}}_2^{+}$ in the formation of the peaks is discussed. It is not clear what mechanism controls the reaction. The data cannot be satisfactorily explained with either the spectator‐stripping or the Langevin model.