Several approaches to ion activation in tandem mass spectrometry have been developed in recent years for use in ion trapping instruments that allow for conditions to be reached wherein rates of ion activation and deactivation are comparable. These approaches are deÐned as slow heating methods and include continuous-wave laser infrared multiphoton dissociation, dissociation driven by blackbody radiation, quadrupole ion trap collisional activation and sustained o †-resonance irradiation in ion cyclotron resonance mass spectrometry. In the limiting case in which ion activation and deactivation rates are equal, a steady-state parent ion internal energy distribution is achieved and the kinetics of dissociation can be interpreted in analogy with thermal dissociation. This discussion describes the thermal analogy and the limiting conditions of rapid energy exchange and slow energy exchange along with the possible ramiÐcations for dissociation rates and product ion spectra. The Ðgures of merit that the various slow heating methods share as a class of activation methods are also discussed. The purpose of this perspective is to provide a frame-of-reference from which slow heating methods can be considered. Such methods are seeing increasing use as the number of ion trapping instruments grows and have shown remarkable success with dissociation of high-mass ions.
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