Reaction dynamics for the [NNO] system from state-resolved and coarse-grained models

Area of Science:

• Chemical Kinetics
• Computational Chemistry
• Atmospheric Chemistry

Background:

• The NO + N reaction is crucial in atmospheric and combustion processes.
• Accurate modeling of this reaction requires high-level potential energy surfaces (PESs).
• Previous studies often relied on simplified rate expressions, potentially missing key dynamic effects.

Purpose of the Study:

• To investigate the dynamics of the NO(X2Π) + N(4S) ↔ N2(X1Σg+) + O(3P) reaction.
• To compare state-to-state (STS) dynamics with Arrhenius-based rates using two distinct high-level PESs.
• To elucidate the role of non-equilibrium energy flow in reaction completeness.

Main Methods:

• Utilized two high-level potential energy surfaces: one using reproducing kernel Hilbert space (RKHS, PESB) and another using permutationally invariant polynomials (PIPs, PESM).
• Performed state-to-state (STS) dynamics calculations and compared them with Arrhenius-based rates.
• Incorporated full dissociation asymptotically to ensure correct stoichiometry.

Main Results:

• Ignition points were consistent (~10^-6 s) across methods and PESs, regardless of reverse rate assumptions.
• STS dynamics predicted complete NO to N2 conversion, while Arrhenius rates showed incomplete conversion.
• Non-equilibrium energy flow and state dynamics were identified as critical factors for complete turnover.
• Concentration profiles showed consistency over 14 orders of magnitude in time when using STS information.

Conclusions:

• State-to-state dynamics provide a more accurate description of the NO + N reaction compared to Arrhenius rates.
• Non-equilibrium effects significantly influence reaction completeness and require state-based treatment.
• The choice of PES had minimal impact on species dynamics when STS information was employed.