COLTRAP: a 22-pole ion trapping machine for spectroscopy at 4 K

Two similar 4 K 22-pole trapping machines have been recently completed in our laboratory. As a first experimental test in one of them, CH5+ and H3O+ ions have been trapped in the presence of helium gas at 3.8 K and the kinetics and temperature dependence of He tagging investigated. A first shell closure with 5 and (3 + 2) attached He atoms, respectively, is observed for both species. Applying IR radiation in the 3 mu m region, helium attachment to CH5+ is hindered by exciting CH-stretches of CH5+ prior to attachment. The resulting spectroscopic signal shows that the kinetic temperature of the stored CH5+ ensemble is below 12 K.