A consistent explanation of seemingly inconsistent experimental and theoretical data for N₂O + O via MultiScale Informatics

The N₂O + O reaction plays a critical role in NO_x formation at high pressures and low peak temperatures, in the “dark zone” region of deflagration waves of organic energetic materials, and in N₂O consumption in NH₃ combustion. While the rate constant for N₂O + O = NO + NO (R3) is considered reasonably well established, viewpoints regarding the rate constants for N₂O + O = N₂ + O₂ (R2)—and even the main products of the N₂O + O reaction—have not reached a consensus, with studies from the past few years continuing to reach drastically different conclusions. To date, no single model has been presented that can reproduce all key datasets on both sides of the debate. Using the MultiScale Informatics (MSI) approach, we identified a model consistent with a vast catalog of theoretical and experimental data previously used to determine rate constants for R2, R3, and other key reactions influencing experimental interpretations. Notably, this MSI model (presented herein) reproduces all experimental datasets previously used to anchor low-activation-energy k₂ expressions that greatly favor R2 at intermediate temperatures. However, its kinetic parameters are also consistent with theoretical calculations that instead show high activation energy for R2 and k₂ values many orders of magnitude lower—such that R3 is the main channel at essentially all temperatures. This model is also consistent with our new experimental data (presented in our companion paper) at optimally selected conditions that avoid the interpretation ambiguities that have hindered definitive conclusions from previous experimental data. The present analysis elucidates the role of secondary reactions that would have artificially inflated the apparent k₂/k₃ ratio previously deduced from experiments in a manner that may not have been detectable from even multi-species measurements at typical conditions—and may, therefore, explain the persistent historical difficulties in establishing the main products of N₂O + O. Novelty and significance statement Despite decades of research, viewpoints regarding the rate constants for N₂O + O = N₂ + O₂ (R2)—and even the main products of the N₂O + O reaction—have not reached a consensus, with studies from the past few years still reaching drastically different conclusions. To date, no single model has been presented that can reproduce all key datasets on both sides of the debate. Here, we present a single model consistent with a vast catalog of theoretical and experimental data, including all experimental datasets previously used to anchor low-activation-energy expressions for k₂ that greatly favor R2 as the main channel at intermediate temperatures—but with kinetic parameters consistent with theoretical calculations that instead show high activation energy for R2 and N₂O + O = NO + NO (R3) as the main channel at essentially all temperatures.