S303
MPI-K, Heidelberg, Germany
In the CSR at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany, a cryogenic electrostatic storage ring for ions up to 300 keV kinetic energy per charge,* a merged and velocity-matched electron beam was used to cool the rotational states of CH+ molecular ions in a 300 keV stored beam. Diagnostics of the relative populations in the J = 0, 1 and 2 rotational levels was achieved by photodissociation in a laser beam with a wavelength close to the CH+ dissociation threshold. During a storage time up to 10 minutes, slow spontaneous rotational cooling to the J = 0 ground state occurs by radiative emission of rotationally excited CH+ ions. Applying electrons in the electron cooling geometry (11.8 eV beam energy) at a density near 7·10+5 per cm³ and a temperature near 2.3 meV boosted the rotational cooling rate by a large factor (~4). Using the laser-based rotational population measurements, the electron-induced rotational cooling rates could be measured.** This presents the first detailed measurement of rotationally inelastic collision cross sections on a molecular ion, as important for the diagnostics of cold astrophysical media. - Presented for the research team.**
* R.v.Hahn et al., Rev. Sci.Instr. 87, 063115 (2016)
** Á.Kálosi, M.Grieser, R.v.Hahn, U.Hechtfischer, C.Krantz, H.Kreckel, D.Müll, D.Paul, D.W.Savin, P.Wilhelm, A.Wolf, O.Novotný, submitted
