Philip D. Pacey
Adjunct Professor
BSc (McGill), PhD (Toronto)
E-mail: philip.pacey@dal.ca
Phone: (902) 494-3334
Fax: (902) 494-1310
Research Interests: Temperature dependence of reaction rates; gas sensors; nanotubes and nanodrops.
Ever since the discovery of fire, people have been fascinated by its orange glow. What is the source of the particles which dance so brightly in a fire's heat? We know the particles are predominantly carbon, but we don't know how they form. The answer to this question is important. If carbon particles escape from the flame, they become soot, a serious pollutant. In industrial processes, carbon forms coke deposits, which interfere with efficient production. On the other hand, carbon formation is necessary in the production of carbon black and in chemical vapour deposition on solid objects.
We are taking several approaches in trying to unravel this mechanism. One postulated pathway has acetylene as a key intermediate. We have shown acetylene reacts by a free radical mechanism, and that it can lead directly to the formation of carbon nanotubes, which may have important applications in electronics. Another possible pathway has polynuclear aromatic hydrocarbons as important intermediates. Using transmission electron microscopy, we have observed the formation of a fog of nanoscale droplets of these hydrocarbons at high temperatures and have observed their fluoresence spectrum for the first time.
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Professor Philip Pacey with members of his research
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Study of the rates of chemical reactions at high temperatures also provides information about reacting species, intermediate between reactants and products. Picogram gas chromatography, mass spectrometry and electron spin resonance spectroscopy are used with fast flow systems in which the concentrations of intermediates have not reached their steady-state values. Intermediate concentrations as small as 10-13 mol L-1 have been measured. Absolute rate constants are determined for elementary processes. Several of these processes are found to exhibit curved Arrhenius plots. Theoretical work is directed toward understanding Arrhenius plot curvature. By studying the shapes of Arrhenius plots, Dr. Pacey and his group learn more about the nature of the reactive event itself. This experimental and theoretical information is revealing some of the secrets of interatomic forces during reactions, such as the thicknesses of activation barriers and the first experimental values of the bending frequencies of transition states.
