The McMahon group investigates structures, energetics and reaction dynamics of gaseous ions. The majority of our work uses high pressure mass spectrometry (HPMS) to explore cluster ions. HPMS is uniquely suited for determining the energetics of gaseous ion-molecule equilibria, particularly those associated with ion-molecule clustering and exchange reactions. Using this technique we have amassed a considerable database for the energetics and kinetics of a wide variety of cluster species.

Over the past decade, we have also used the free electron laser at the Centre Laser Infrarouge d’Orsay (CLIO, Université Paris-Sud XI) to perform infrared multiple photon dissociation (IRMPD) spectroscopy experiments in the mid-infrared ‘fingerprint’ region. This is a form of consequence spectroscopy that allows detailed ion structures to be identified from characteristic absorption frequencies. These experiments are supported by high-performance quantum chemical calculations at Waterloo that help reveal the intrinsic properties of gas-phase ions. Current projects are listed below.

High Pressure Mass Spectrometry

Infrared Spectroscopy of Biological Ions

Predicting Ion Behaviour Computationally


  • VG Instruments MM 8-80 magnetic mass spectrometer with high-pressure source.
  • VG Instruments 70-70 double focusing analytical mass spectrometer with high-pressure source.