Motional Mode Conversion in the Orbitrap
- 1Laguna Niguel, California, USA, 92677
Abstract
Resonant coupling between motional modes has played an important role in trapped-ion physics and Fourier transform ion cyclotron resonance (FTICR) mass spectrometry, enabling ion manipulation, cooling, centering, and precision measurements. In contrast, controlled mode conversion in the Orbitrap mass analyzer has received little attention. Here we develop a general theory of motional mode conversion in the Orbitrap and identify three classes of resonant transfer: radial-axial (), azimuthal-axial (), and radial-azimuthal () conversion. Coupling potentials for the three conversion processes are derived from symmetry considerations and analyzed using an action-angle description of Orbitrap dynamics. Numerical simulations demonstrate coherent transfer between the participating motional modes and confirm the predicted resonance conditions. A central result is that conversion processes involving the radial mode require rotating-frame formulations to maintain phase coherence with the instantaneous radial motion direction of the ion in orbit, whereas azimuthal-axial conversion can be described directly in the laboratory coordinate frame. The simulations further demonstrate two potentially useful ion-manipulation techniques. Radial-azimuthal and radial-axial conversions provide two complementary routes to Orbitrap circularization, whereas radial-axial and azimuthal-axial conversions provide two complementary routes to axial centralization. These operations may be combined with azimuthal dipolar excitation/de-excitation, or additional mode-conversion steps to prepare ions in standardized trajectories prior to image-current detection of the azimuthal rotation. The concepts developed here establish a theoretical foundation for additional active control of Orbitrap ion motion beyond the methods provided by traditional dipolar excitation and suggest new opportunities for ion manipulation.
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BibTeX
@misc{guan2026motional,
title = {{Motional Mode Conversion in the Orbitrap}},
author = {Shenheng Guan},
howpublished = {ChemRxiv},
year = {2026},
month = oct,
doi = {10.26434/chemrxiv.15009934/v1},
url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15009934/v1},
note = {CC BY},
}
RIS
TY - UNPB
TI - Motional Mode Conversion in the Orbitrap
AU - Shenheng Guan
PY - 2026
DA - 2026/10/05
PB - ChemRxiv
DO - 10.26434/chemrxiv.15009934/v1
UR - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15009934/v1
AB - Resonant coupling between motional modes has played an important role in trapped-ion physics and Fourier transform ion cyclotron resonance (FTICR) mass spectrometry, enabling ion manipulation, cooling, centering, and precision measurements. In contrast, controlled mode conversion in the Orbitrap mass analyzer has received little attention. Here we develop a general theory of motional mode conversion in the Orbitrap and identify three classes of resonant transfer: radial-axial (), azimuthal-axial (), and radial-azimuthal () conversion. Coupling potentials for the three conversion processes are derived from symmetry considerations and analyzed using an action-angle description of Orbitrap dynamics. Numerical simulations demonstrate coherent transfer between the participating motional modes and confirm the predicted resonance conditions. A central result is that conversion processes involving the radial mode require rotating-frame formulations to maintain phase coherence with the instantaneous radial motion direction of the ion in orbit, whereas azimuthal-axial conversion can be described directly in the laboratory coordinate frame. The simulations further demonstrate two potentially useful ion-manipulation techniques. Radial-azimuthal and radial-axial conversions provide two complementary routes to Orbitrap circularization, whereas radial-axial and azimuthal-axial conversions provide two complementary routes to axial centralization. These operations may be combined with azimuthal dipolar excitation/de-excitation, or additional mode-conversion steps to prepare ions in standardized trajectories prior to image-current detection of the azimuthal rotation. The concepts developed here establish a theoretical foundation for additional active control of Orbitrap ion motion beyond the methods provided by traditional dipolar excitation and suggest new opportunities for ion manipulation.
ER -