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MO: Molekülphysik
MO 2: Stoßprozesse
MO 2.5: Talk
Monday, March 16, 1998, 15:00–15:15, M627
Measurements of the cross sections of electron impact ionization and dissociative ionization of interstellar molecules — •Cechan Tian and C.-R. Vidal — Institut f"ur extraterrestrische Physik, Postfach 1603, D-85740 Garching
The electron impact ionization and dissociative ionization of molecules are important processes in planetary and cometary atomspheres and plasmaprocessing [1]. The cross sections of the electron impact ionization anddissociative ionization of interstellar molecules such as CO, CO2, CH4, and C2H2 have been measured with a specially designedfocusing time-of-flight mass spectrometer. The molecules are ionized incrossed molecular and electron beams. The focusing characteristic of themass spectrometer generates the ions close to the axis and focuses theenergetic ions back to the detector. We demonstrate the complete collection of all the ionic fragments experimentally by observing the deflection curves.We therefore measure the cross sections conclusively. By analysing the time-of-flightprofiles of the mass peaks, we obtained the kinetic energy distributions associatedwith the ions produced in the dissociative ionization. The kinetic energydistributions help to understand the dynamics of the dissociative ionization and the reason why most of the previous measurements are unreliable.
[1] Comment. At. Mol. Phys. 11, 177 (1988)