# CCL: Pressure dependence in reaction rate kinetics calculations

*From*: "Ted Dibble" <tsdibble#syr.edu>
*Subject*: CCL: Pressure dependence in reaction rate kinetics
calculations
*Date*: Wed, 23 Mar 2011 11:28:45 -0400

Sent to CCL by: "Ted Dibble" [tsdibble{:}syr.edu]
The answers to your questions can be found in most textbooks. Start with a
physical chemistry textbook for the basics, and look in a graduate kinetics
textbook for fuller explanations. Look for the Lindeman or Lindeman-Hinshelwood
mechanism.
The three-body reaction is the net reaction including the third body, e.g.:
ClO + NO2 + M = ClONO2 + M
where M is the third body, and [M] corresponds to the total concentration of
gas phase species. This is in contrast to the elementary reactions:
ClO + NO2 -> ClONO2*
ClONO2* -> ClO + NO2
ClONO2* + M -> ClONO2 + M
Please note: TST applies where there is a Boltzmann distribution of energy,
which corresponds to the high-pressure limit rather than the low-pressure
limit.
To calculate rate constants versus pressure, see the UNIMOL package, made
available at http://www.frad.t.u-tokyo.ac.jp/miyoshi/ssumes/index.html
Good luck!
Theodore S. Dibble
Chemistry Department
SUNY-Environmental Science and Forestry
1 Forestry Drive
Syracuse, NY 13210
(315) 470-6596
(315) 470-6856 (fax)
http://www.esf.edu/chemistry/faculty/dibble.htm
> "RD Miles rdmsgl!A!gmail.com" wrote:
>
> Sent to CCL by: RD Miles [rdmsgl^gmail.com]
> --0015173fe52af75fe4049efe5381
> Content-Type: text/plain; charset=ISO-8859-1
>
> I have been working on calculating reaction rate constants at the low
> pressure limit using TST type methodologies. However, I need to understand
> how to transition into calculations for high pressure systems.
>
> Could you recommend any references that deal specifically with the pressure
> dependence of reaction rate constants, and how it is addressed in
> computational chemistry?
>
> Questions I have are:
>
> - Can TST based methods be adapted to high pressure systems?
> - What is meant by "3 body reactions" in many kinetics
mechanisms?
> - What is meant by the pressure dependence "fall-off" in some
reaction
> rate constant descriptions?
>
> Any help on this subject would be greatly appreciated.
>
> -RD