Skip to content

Measurement of the orientation of buffer-gas-cooled, electrostatically-guided ammonia molecules

Research output: Contribution to journalArticle

  • Edward W. Steer
  • Lorenzo S. Petralia
  • Colin M. Western
  • Brianna R. Heazlewood
  • Timothy P. Softley
Original languageEnglish
Pages (from-to)94-102
Number of pages9
JournalJournal of Molecular Spectroscopy
Early online date11 Nov 2016
DateAccepted/In press - 10 Nov 2016
DateE-pub ahead of print - 11 Nov 2016
DatePublished (current) - Feb 2017


The extent to which the spatial orientation of internally and translationally cold ammonia molecules can be controlled as molecules pass out of a quadrupole guide and through different electric field regions is examined. Ammonia molecules are collisionally cooled in a buffer gas cell, and are subsequently guided by a three-bend electrostatic quadrupole into a detection chamber. The orientation of ammonia molecules is probed using (2+1) resonance-enhanced multiphoton ionisation (REMPI), with the laser polarisation axis aligned both parallel and perpendicular to the time-of-flight axis. Even with the presence of a near-zero field region, the ammonia REMPI spectra indicate some retention of orientation. Monte Carlo simulations propagating the time-dependent Schrödinger equation in a full basis set including the hyperfine interaction enable the orientation of ammonia molecules to be calculated – with respect to both the local field direction and a space-fixed axis – as the molecules pass through different electric field regions. The simulations indicate that the orientation of ∼ 95% of ammonia molecules in J K = 1 1 could be achieved with the application of a small bias voltage (17 V) to the mesh separating the quadrupole and detection regions. Following the recent combination of the buffer gas cell and quadrupole guide apparatus with a linear Paul ion trap, this result could enable one to examine the influence of molecular orientation on ion-molecule reaction dynamics and kinetics.

    Research areas

  • Cold molecules, Quadrupole guide, Alignment, Ammonia, Polarisation

Download statistics

No data available



  • Full-text PDF (final published version)

    Rights statement: This is the final published version of the article (version of record). It first appeared online via Elsevier at Please refer to any applicable terms of use of the publisher.

    Final published version, 1.85 MB, PDF document

    Licence: CC BY


View research connections

Related faculties, schools or groups