Abstract The experimental results for H+5 cluster ions are reported . The formation an d dissociation of H+5 cluster ions were discussed. Accord ing to theory, sta ble H+n cluster ions may be formed by H+3< /sub> core with one or more H 2 molecule. On the other hand, there exist conditions for the reactio n of H+3 and H2 in a rf ion source. In the experiments, the ion beam was accelera ted by van de Graff and selected by 90° analysis magnet in the condition of cur rent for mass number 5, and then diffracted by 20° analysis magnet, the energy spectrum of ion beam was obtained. From the spectrum, it is found that H+ sup>5 cluster ions may be formed from the ion-molecular interaction between H+3 ion and H2 neutral molecule in rf ion source and that there may exist H3 and H4 neutral clusters among the products of H+5 c luster ions.