[franco81]

Hello everybody,

I have no chemical university-background, so my question is more something as "where should I look for..." question.
I need to give an estimation (within a factor 2 to 5) of a kinetic rate for the following reactions:
1) N2O(v1,v2,v3) + M -> N2 + O + M (where M is generic)
2) N2O(v1,v2,v3) + O -> N2 + O2
 
In this case the thermal reaction rate should be enhanced by the vibronic excitation state of the molecule.
I know there is the Polanyi rule for bi-atomic molecules, is there a similar rule for triatomic?
I believe also there are software that could be used for the purpose, without getting into to much quantum-chemical calculations, maybe?

Any suggestion is greatly appreciated, thank you very much!

[Plontaj]

Hello

I believe also there are software that could be used for the purpose, without getting into to much quantum-chemical calculations, maybe?

I don't think so. I'm sorry.

At the beginning:
In the chemical kinetic the basic assumption is that elementary reactions can be written according with law of mass action. If they are elementary, they have one active complex - one activation energy. So for 1st irreversible reaction we can write:
r1=k1*[N2O]*[M]
and for 2nd reaction:
r2=k2*[N2O]*[ O ]

If the interesting us value is N2O rate conversion, the expression for it is:
d[N2O]/dt = - r1 - r2

k1 and k2 are kinetic constants, they depend from temperature according Arrhenius expression:
k = k0 * exp (-Ea/(RT)), k0 - frequency of collisions factor, exp(-Ea/(RT)) - effective collisions factor.

or quite similar experimental expression without references to phisic values:
k = A * T^B * exp (-C/(RT))

The experimental values of k and information about the molecular of reaction you can get from databases like: http://kinetics.nist.gov.

I've checked those reactions and they are available in this database:

r1: http://kinetics.nist.gov/kinetics/ReactionSearch?r0=10024972&r1=0&r2=0&r3=0&r4=0&p0=7727379&p1=17778802&p2=0&p3=0&p4=0&expandResults=true&
Important will be in your case the bath gas, I think.

r2: http://kinetics.nist.gov/kinetics/ReactionSearch?r0=10024972&r1=17778802&r2=0&r3=0&r4=0&p0=7727379&p1=7782447&p2=0&p3=0&p4=0&expandResults=true&

Good luck

PS. If I can ask, what are the reasons you are interested in this reaction?

[franco81]

Hello!

Thanks for the reply; I'm aware of the thermal rate of decomposition and recombination of N2O, there are also a few very interesting theoretical works: 1) the paper from Jill and Laidler (1958) that compare the experimental thermal rate with Slater and HKRR unimolecular decomposition theory; the second is from Stern and Eyring which derives the thermal rate in the framework of early Transition State Theory (this would seem a viable approach). I know there has been an interest in the 70', especially for laser applications, and I'm scanning many textbook but without luck for now.
I'm interested in this topic because I work with plasma, which have the ability to excite vibrational degree of freedom inside the molecule promoting 'catalytic effects' in chemical reactions.
Thanks anyway.