Ejection of Coulomb Crystals from a Linear Paul Ion Trap for Ion-Molecule Reaction Studies

Research output: Contribution to journalArticlepeer-review


  • K. A E Meyer
  • L. L. Pollum
  • L. S. Petralia
  • A. Tauschinsky
  • C. J. Rennick
  • B. R. Heazlewood


Coulomb crystals are being increasingly employed as a highly localized source of cold ions for the study of ion-molecule chemical reactions. To extend the scope of reactions that can be studied in Coulomb crystals - from simple reactions involving laser-cooled atomic ions, to more complex systems where molecular reactants give rise to multiple product channels - sensitive product detection methodologies are required. The use of a digital ion trap (DIT) and a new damped cosine trap (DCT) are described, which facilitate the ejection of Coulomb-crystallized ions onto an external detector for the recording of time-of-flight (TOF) mass spectra. This enables the examination of reaction dynamics and kinetics between Coulomb-crystallized ions and neutral molecules: ionic products are typically cotrapped, thus ejecting the crystal onto an external detector reveals the masses, identities, and quantities of all ionic species at a selected point in the reaction. Two reaction systems are examined: the reaction of Ca+ with deuterated isotopologues of water, and the charge exchange between cotrapped Xe+ with deuterated isotopologues of ammonia. These reactions are examples of two distinct types of experiment, the first involving direct reaction of the laser-cooled ions, and the second involving reaction of sympathetically-cooled heavy ions to form a mixture of light product ions. Extensive simulations are conducted to interpret experimental results and calculate optimal operating parameters, facilitating a comparison between the DIT and DCT approaches. The simulations also demonstrate a correlation between crystal shape and image shape on the detector, suggesting a possible means for determining crystal geometry for nonfluorescing ions.


Original languageEnglish
Pages (from-to)12449-12456
Number of pages8
JournalThe Journal of Physical Chemistry A
Publication statusPublished - 25 Sep 2015

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