PC GAMESS/Firefly-related discussion club

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Slawomir Janicki
slawomir.janicki@comcast.net

Great help, as always. The decomposition reactions I am interested in occur in catastrophic events (deflagrations, explosions), so the pressure generated is usually very high. From brief search on the RRKM theory, at high pressures it is equivalent to the transition state theory (for example see here: http://vallance.chem.ox.ac.uk/pdfs/UnimolecularReactionNotes.pdf). Is this correct?

>Another point is that you need to be able to describe barriers
>of different pathways of decomposition within approximately the same
>accuracy...

When I use the same level of theory and thight convergence criteria I should be able to get to the same accuracy of enthalpy. The entropy error could be different for different modes because of internal rotations. I was planning to correct that using rotation barriers calculated from unrelaxed PES for all rotors. Is this close enough?

And last, which reaction paths would I miss?

Slawomir

On Tue Oct 20 '09 6:41pm, Alex Granovsky wrote
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>Hi,

>>My initial idea is to follow IRC along all vibrations of the starting molecule. Most vibration probably would not result in a decomposition under these conditions and I would concentrate on those with activation energy under 1000 K. Do you think this is reasonable? Would I miss some paths this way?

>Just my two cents:

>The idea isn't too bad, however you do can miss some pathways of
>decomposition. The unimolecular decay is usually a complex process,
>which includes bimolecular activation stages (e.g., well-known
>RRKM theory is one of the  possible theoretical approaches to
>unimolecular reactions) and then the redistribution of
>vibrational energy.

>Another point is that you need to be able to describe barriers
>of different pathways of decomposition within approximately the same
>accuracy...

>Best,
>Alex Granovsky

>