| 摘要 |
In ion cyclotron resonance spectroscopy, a gaseous sample substance contained in a measuring cell and exposed to a constant magnetic field therein is ionized and is subsequently subjected to an electric HF measuring field oriented orthogonally to the magnetic field. The frequencies of the electric field encompass the frequencies of the cyclotron resonance frequencies of the ions of the sample substance. Sample substances often include ions which are of no interest to the material under study but which produce very strong lines that can be highly disturbing because of the limited dynamics of the spectrometer and, especially, the relatively low concentration of ions in the measuring cell which is necessary to prevent space charge effects. To avoid such disturbances, the sample substance is subjected to a HF selection field, prior to applying the HF measuring field, which selection field includes the cyclotron resonance frequency of at least one of the undesired ion species, for a period of time until the orbital radii of the ions of this kind have reached a magnitude at which the ions collide with the walls of the measuring cell and are thereby ejected. By repeating the process of ionization and elimination of the undesired ions, the concentration of the desired ions in the cell can be increased up to the permissible maximum value, resulting in a substantial increase in the sensitivity of the spectrometer.
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