Hannover 2003 – wissenschaftliches Programm
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MO: Molekülphysik
MO 2: Chemische Reaktionen, Energietransfer
MO 2.5: Vortrag
Montag, 24. März 2003, 17:30–17:45, B 302
Formation of interstellar methanol via radiative association — •Alfonz Luca, Didier Voulot, and Dieter Gerlich — Department of Physics, Technical University Chemnitz, Germany
It is an open question, whether methanol is formed via reactions on surface of ice particles or in gas phase under the conditions prevailing in interstellar clouds. One proposed mechanism is radiative association of CH3+ + H2O followed by electron-ion recombination. A low temperature radio-frequency 22-pole ion trap has been combined with a molecular beam for studying ion-molecular association processes at low number densities and at temperatures where an effusive gas inlet cannot be used due to condensation. CH3+ has been stored at He number densities ranging from 7 × 1013 cm−3 down to 5 × 1011 cm−3. Under these conditions collisions between the ions and the H2O occur at an effective temperature of 50 K. The three body association rate coefficient has been determined as k3 = (5.8 ± 0.4) × 10−25 cm6s−1. For radiative association, an upper limit for the rate coefficient has been estimated from the measurements, kr < 2 × 10−12 cm3s−1. This is at least one order of magnitude smaller than the value currently used in model calculations. For future experiments it is planed to apply this method to other systems e.g. the association of CH3+ + CO.