Simultaneous monitoring of the radial modes of the ion motion and their manipulation in Penning traps by FT-ICR mass spectrometry

It is demonstrated how FT-ICR MS can be used to monitor both the coherent magnetron motion and the cyclotron motion of ions stored in a Penning trap. By use of the ICR signal intensity at the magnetron frequency, ν−, and the reduced cyclotron frequency, ν+, the manipulation of the ion motion by dipolar, quadrupolar, and octupolar excitation has been followed. In particular, the conversion between the magnetron and the cyclotron motion by quadrupolar and octupolar excitation at the corresponding resonance frequencies νc = ν+ + ν− and 2νc, respectively, has been observed by detection of the magnetron and the cyclotron signal. While the ion motion under the influence of a quadrupolar excitation has already been studied extensively, the octupolar excitation has been introduced only recently. As compared to other techniques, such as the time-of-flight ion-cyclotron-resonance detection method, FT-ICR MS allows to simultaneously investigate the influence of an excitation on the cyclotron und the magnetron motional modes.