Hi all,
I am working with MESMER to calculate the overall rate constant of a multistep reaction such as
R1+R2 (0.0+0.0) -> Comp1(-3.5) -> TS (5.0) -> Prod1(-15.5)
The numbers in the parenthesis represent their zero-point corrected energies in kcal/mol unit. Here the first step (i.e. R1+R2 -> Comp1) is a bimolecular step and the second step (i.e. Comp1->TS -> Prod1) is an unimolecular reaction step.
In experimental conditions, R1 has excess vibrational energy (R1 * ) around 10 kcal/mol. It is well known that the RRKM rate constant for the second step (i.e. Comp1 -->TS --> Prod1) will be obtained when the Comp1 has excess energy over the TS. Hence how do I put excess vibrational energy on Comp1 when I am dealing with the R1 * + R2 reaction in the MESMER program?
Last edit: SAIKAT SADHUKHAN 2024-10-30
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It might be possible to model this system in MESMER. However, the shallow well and low transition state suggest that there will be convergence of eigenvalues so it is going to be difficult to extract rate coefficients. It may be better to consider a scattering code for this system such as PolyRate. If you would like to pursue this with MESMER. it would us a lot if you could share more details of the system.
With regards, Struan
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Thank You for your time. I am attaching a file for your convenience. I am also attaching a schematic diagram of the problem I have discussed above. Here I want to make R1 as well as comp1 vibrationally excited so that it has sufficient energy over the TS. Can you suggest a way to model this type of reaction in MESMER?
Additionally, I would like to know if the following keywords may come in handy in this case.
1. electronicExcitation
2. Excitation
3. EnergyExcess
Thank-you for sending me your input file. I have made a few changes and run some calculations, the input file and the results are in the attached .zip file. I created an initially excited distribution of the R1 species by shifting a Boltzmann distribution by 3500 cm-1. However, I have not observed any impact of this initial distribution. This can best be seen by inspecting the mesmer_out.xml file in Firefox (see manual for details). As you will see I looked at several sets of conditions to see if these would have an impact on and I also decreased the value of <delta e="">down, and while I found that there was a decrease in the rate of relaxation of R1 as the pressure declined, the time regions between vibrational relaxation and overall reaction did not overlap (see energy diagrams in FireFox) and so there was no impact on the reaction from the initial excitation. I suspect that one must go to even lower pressures, but at this point the concentration of the excess species will become equivalent to that of the bath gas. </delta>
Hi all,
I am working with MESMER to calculate the overall rate constant of a multistep reaction such as
R1+R2 (0.0+0.0) -> Comp1(-3.5) -> TS (5.0) -> Prod1(-15.5)
The numbers in the parenthesis represent their zero-point corrected energies in kcal/mol unit. Here the first step (i.e. R1+R2 -> Comp1) is a bimolecular step and the second step (i.e. Comp1->TS -> Prod1) is an unimolecular reaction step.
In experimental conditions, R1 has excess vibrational energy (R1 * ) around 10 kcal/mol. It is well known that the RRKM rate constant for the second step (i.e. Comp1 -->TS --> Prod1) will be obtained when the Comp1 has excess energy over the TS. Hence how do I put excess vibrational energy on Comp1 when I am dealing with the R1 * + R2 reaction in the MESMER program?
Last edit: SAIKAT SADHUKHAN 2024-10-30
Hello,
Sorry for the slow response to your request.
It might be possible to model this system in MESMER. However, the shallow well and low transition state suggest that there will be convergence of eigenvalues so it is going to be difficult to extract rate coefficients. It may be better to consider a scattering code for this system such as PolyRate. If you would like to pursue this with MESMER. it would us a lot if you could share more details of the system.
With regards, Struan
Thank You for your time. I am attaching a file for your convenience. I am also attaching a schematic diagram of the problem I have discussed above. Here I want to make R1 as well as comp1 vibrationally excited so that it has sufficient energy over the TS. Can you suggest a way to model this type of reaction in MESMER?
Additionally, I would like to know if the following keywords may come in handy in this case.
1. electronicExcitation
2. Excitation
3. EnergyExcess
Last edit: SAIKAT SADHUKHAN 2024-11-06
Hello,
Thank-you for sending me your input file. I have made a few changes and run some calculations, the input file and the results are in the attached .zip file. I created an initially excited distribution of the R1 species by shifting a Boltzmann distribution by 3500 cm-1. However, I have not observed any impact of this initial distribution. This can best be seen by inspecting the mesmer_out.xml file in Firefox (see manual for details). As you will see I looked at several sets of conditions to see if these would have an impact on and I also decreased the value of <delta e="">down, and while I found that there was a decrease in the rate of relaxation of R1 as the pressure declined, the time regions between vibrational relaxation and overall reaction did not overlap (see energy diagrams in FireFox) and so there was no impact on the reaction from the initial excitation. I suspect that one must go to even lower pressures, but at this point the concentration of the excess species will become equivalent to that of the bath gas. </delta>
I hope this helps a little.
Regards, Struan