EVOLUTION OF AN ION CLOUD IN A FOURIER-TRANSFORM ION-CYCLOTRON RESONANCE MASS-SPECTROMETER DURING SIGNAL-DETECTION - ITS INFLUENCE ON SPECTRAL-LINE SHAPE AND POSITION

The factors responsible for temporal variation of the detected frequen cy in an FT ion cyclotron resonance (ICR) spectrometer are analysed. T he time-dependent frequency behaviour is believed to be caused by a ch ange in ion cloud configuration, the number of detected ions, and the ion cloud position in the electric field of the ICR cell. The spectral peak shape is calculated for an ensemble of non-interacting ions dist ributed over amplitudes of axial oscillations. The influence of the Co ulomb interaction on the signal and the spectral peak shape is studied by a computer simulation using a highly parallel computer.