A question about the reaction rate expressions of three-body collisions

[arief...@gmail.com]

Dear Colleagues,

Please have a look at the rates of the following reactions.

#Reaction A:

- equation: H + OH + M <=> H2O + M
  type: three-body
  rate-constant: {A: 2.2e+22, b: -2.0, Ea: 0.0}
  efficiencies: {H2: 0.73, H2O: 3.65, AR: 0.38}

#Reaction B:

- equation: 2 OH (+M) <=> H2O2 (+M)  # Reaction 22
  type: falloff
  low-P-rate-constant: {A: 2.3e+18, b: -0.9, Ea: -1700.0}
  high-P-rate-constant: {A: 7.4e+13, b: -0.37, Ea: 0.0}
  Troe: {A: 0.7346, T3: 94.0, T1: 1756.0, T2: 5182.0}
  efficiencies: {H2: 2.0, H2O: 6.0, AR: 0.7}

Reaction B has two rate-constant expressions. Which is consistent with the theory describing the inclusion of pressure effects on the rate constant.

But reaction A has only one rate-constant expression. Does this mean that the same rate-constant expression used twice? That is once: for k(T) and once for k(P,T)?

Furthermore: in which file of the source code can I see where the rate-constant expressions are implemented?

Best Regards,

Arief

[Mark E. Fuller]

Hi Arief,

These are two different types of reactions, which require different information to describe their behavior across temperature and pressure.

If you are unfamiliar with how three-body and (Troe) falloff reactions differor are defined, see https://cantera.org/science/reactions.html

Kinetics are documented at https://cantera.org/documentation/docs-2.5/sphinx/html/cython/kinetics.html and the reaction types utilized above are documented specifically at

https://cantera.org/documentation/docs-2.5/sphinx/html/cython/kinetics.html#threebodyreaction and

https://cantera.org/documentation/docs-2.5/sphinx/html/cython/kinetics.html#falloffreaction respectively.

[arief...@gmail.com]

Hello Mark,

Many thanks for the clarification!

This is very helpful.

Arief