Dresden 2011 – wissenschaftliches Programm

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MS: Fachverband Massenspektrometrie

MS 4: Precision Mass Spectrometry and Fundamental Applications

MS 4.1: Hauptvortrag

Dienstag, 15. März 2011, 10:30–11:00, GÖR 229

On the interconversion of an ion's motional modes in a Penning trap by quadrupolar and octupolar rf-fields — •Martin Kretzschmar — Institut für Physik, Johannes Gutenberg-Universität, 55099 Mainz, Germany

Penning trap mass spectrometry rests on the precise determination of an ion's cyclotron frequency. Part of the measurement procedure is the resonant conversion of magnetron motion into cyclotron motion by means of external quadrupolar or octupolar rf-fields.

I shall discuss the interconversion of the motional modes in a quantum mechanical formulation in conjunction with the rotating wave approximation. This permits the identification of the effective interactions responsible for the conversion process. The concept of the Bloch vector is introduced and applied to the conversion process to derive the excitation curve at the exact resonance frequency, and the conversion profile as a function of detuning.

The main emphasis shall be on novel results relating to the conversion by octupolar rf-fields with a frequency equal to twice the cyclotron frequency. Analytical solutions for the Bloch vector in terms of Jacobi elliptical functions shall be presented, the dependence of excitation curves and conversion profiles on the initial phases and amplitudes of the ion motional modes and of the octupolar field shall be discussed. The most remarkable feature of octupolar excitation is the extreme narrowness of the resonant conversion profiles, promising the possibility of very high mass resolution in future experiments. The theoretical results shall be compared to existent experimental data.