München 2004 – scientific programme
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MO: Molekülphysik
MO 18: Stossprozesse, Energietransfer
MO 18.6: Talk
Thursday, March 25, 2004, 17:45–18:00, HS 355
Chemical probing spectroscopy of H3+ in a 22-pole ion trap — •J. Mikosch1,2, H. Kreckel1, R. Wester2, J. Glosík3, R. Plašil3, D. Gerlich4, D. Schwalm1, and A. Wolf1 — 1Max-Planck-Institut für Kernphysik, 69117 Heidelberg — 2Physikalisches Institut, Universität Freiburg, 79104 Freiburg — 3Charles University Prague, Czech Republic — 4Institut für Physik, TU Chemnitz, 09107 Chemnitz
The triatomic hydrogen molecular ion H3+ is the dominant ion in hydrogen plasmas at moderate temperatures. Consequently it plays important roles in many fields from interstallar chemistry and planetary atmospheres to cooling processes in fusion plasmas and model calculations for polyatomic molecular ions. The recombination rate of H3+ with electrons is one of the crucial parameters for the modelling of interstellar clouds and it is still a controversial issue.
In the last years a cryogenic 22-pole trap project was launched at the MPI für Kernphysik, to create a temperature-variable source of H3+ for electron recombination experiments at the TSR storage ring. Here we report a new method for H3+ spectroscopy that operates at low number densities and relies on the reaction H3++Ar—→ArH++H2 which is endoergic by 0.57 eV and thus proceeds only for H3+ states with v≥ 2. In the experiment about 500 H3+ molecules are stored in the ion trap together with Ar buffer gas; a tunable diode laser excites H3+ from its lowest rotational states to v=3 from where immediately ArH+ is formed, which is detected by a mass spectrometer ion detector. Relative line strengths and Doppler widths are used as a thermometer of the ion temperature in the 22-pole trap.