ReactionMechanismGenerator / ReactionMechanismGenerator/RMG-Py

singlet oxygen getting added to mechanism through decay operation

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#2,849 3 comments 0 reactions 1 assignee View on GitHub

@sevyharris is already working on this.

Since Sep 19, 2025.

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Description

Bug Description

I have a recent butane combustion mechanism that forms singlet oxygen through this R Recombination reaction:

! Reaction index: Chemkin #1259; RMG #87
! Template reaction: R_Recombination
! Flux pairs: OH(15), OH(15); O2(2), OH(15);
! Estimated from node Root_N-1R->H_N-1CNOS->N_1COS->O_Ext-1O-R_N-2R->C_N-3R!H->N_2OS->O in family R_Recombination.
! Multiplied by reaction path degeneracy 2.0
O2(2)+OH(15)<=>O2(52)+OH(15)                        4.000000e+13 0.000     22.540

What happens is it forms the [O]OO radical and then decays according to the rmgpy.rmg.decay template.

Image

This then causes more problems in the mechanism because it starts reacting the singlet oxygen with everything else.

How To Reproduce

chemkin file
input file
RMG log
species dictionary

Expected Behavior

I'm using the Burke O2+H2 seed mechanism, so I don't really want RMG guessing more O2 reactions. I don't expect singlet oxygen to end up in this mechanism.

Installation Information

Describe your installation method and system information.

Additional Context

I'm not sure what the right approach is to fixing this. Some options from what I think are best to worst:

  1. Forbid singlet oxygen as a possible decay product in the decay module
  2. Forbid the undecayed [O]OO radical as a product in the R Recombination family
  3. Add a calculation of this reaction to R Recombination depository (or a copy of the reaction with zero kinetics) so RMG knows the rate should be much slower

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