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SUMMARY:Timescales of chemical reactions - Prof. Mike J Pilling CBE\, Scho
 ol of Chemistry\, University of Leeds
DTSTART:20111025T151500Z
DTEND:20111025T161500Z
UID:TALK34232@talks.cam.ac.uk
CONTACT:Alice Wood
DESCRIPTION:Chemical reactions occur on timescales from femtoseconds to ma
 ny\nyears. Some reactions occur before the energy can be randomly\ndistrib
 uted in the reacting molecule\; the reaction between\ncyclopentyne and eth
 ene\, for example\, requires a dynamical\ndescription in order to understa
 nd the mechanism. For many other\nreactions\, occurring on longer timescal
 es\, energy is randomly\ndistributed in the reacting molecule\, but not eq
 uilibrated with the\nbath gas\, and it is necessary to consider the intera
 ction between\ncollisional energy transfer and reaction\, using a master e
 quation\napproach. Such an approach may be necessary even in solution phas
 e reactions\, despite the high collisional frequency\, as illustrated by t
 he reaction between propene and BH3.\n\nGas phase reactions following the 
 association of two molecules can\nlead\, on a single chemical timescale\, 
 to the association product. In\nother cases\, such as the reaction between
  an organic radical and O2\,\nthe reaction may involve several isomers\, a
 nd can lead to dissociation to form bimolecular products. There are now se
 veral chemical timescales\, which depend on the details of the isomerisati
 on\, dissociation and energy transfer processes occurring in the reacting 
 system. Examples will be drawn from combustion and atmospheric chemistry. 
 Solution of the master equation is the key to understanding these timescal
 es and interpreting experimental results to obtain the underlying chemical
  kinetics and mechanism.\n\nTimescales of complex sequences of chemical re
 actions can be\ninterpreted in a similar way\, but now using the Jacobian 
 of the\nsystem. There is a distinction between the chemical lifetime – t
 he\nreciprocal of the reactant’s overall pseudo first-order rate constan
 t\nfor loss – and the system timescales\, as has been appreciated for ma
 ny years for methane in the atmosphere. Other examples will be briefly dis
 cussed.
LOCATION:Pfizer Lecture Theatre\, Department of Chemistry
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