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Updated: May 26, 2026
08:46
Methane Hydrate Crystallization on Sessile Water Droplets
Published on: May 26, 2021
Ionization of methane clusters in helium nanodroplets
Christian Leidlmair1, Peter Bartl, Harald Schöbel
1Institute for Ion Physics und Applied Physics, University of Innsbruck, Innsbruck, Austria.
Summary
Electron ionization of helium droplets with methane clusters reveals unique magic numbers in cluster ions. This study also reports the first observation of methane cluster dications formed via a novel two-step mechanism.
Area of Science:
- Physical Chemistry
- Chemical Physics
- Materials Science
Background:
- Helium droplets are utilized as a unique medium for studying the properties of embedded molecules and clusters.
- Methane clusters provide a model system for investigating fundamental cluster physics and chemistry.
Purpose of the Study:
- To investigate the electron ionization of helium droplets doped with methane clusters for the first time.
- To characterize the resulting cluster ions, including unprotonated and protonated species, and dications.
- To explore the formation mechanisms and structural properties of methane clusters.
Main Methods:
- High-resolution mass spectrometry was employed to analyze the products of electron ionization.
- Analysis of mass spectra to identify dominant ion products and magic numbers.
- Comparison of experimental results with theoretical models for cluster stability and formation.
Main Results:
- Observed dominant unprotonated (CH(4))(n)(+) and protonated CH(5)(+)(CH(4))(n-1) cluster ions.
- Identified magic numbers in mass spectra, broadly consistent with icosahedral shell closings, with unusual differences between ion types.
- Reported the first observation of (CH(4))(n)(2+) dications (n≥70) formed via a two-step charge transfer and Penning ionization mechanism.
Conclusions:
- The study provides novel insights into the structure and stability of methane clusters formed within helium droplets.
- The observed magic numbers and differences suggest specific shell closing effects and potential structural variations.
- The discovery of a two-step mechanism for dication formation expands the understanding of ionization processes in molecular clusters.
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