We present molecular-scale computational rotational-vibrational relaxation studies for N 2 , O 2 , and NO . Characteristic relaxation times for diatom-diatom and diatom-atom interactions are calculated using direct molecular simulation (DMS), with ab initio potential energy surfaces (PESs) as the sole model input. Below approximately 8000 K our N 2 N 2 , O 2 O 2 , and O 2 N 2 vibrational relaxation times agree well with the Millikan–White (M&W) correlation, but gradually diverge at higher temperatures. Park’s high-temperature correction produces a relatively steeper temperature rise compared to our estimates. DMS further shows that, with increasing temperature, the gap between vibrational and rotational relaxation times shrinks for all species. At T > 30,000 K their magnitudes become comparable and a clear distinction between both energy modes becomes meaningless. For other interactions, our DMS results differ substantially from the M&W correlation, both in magnitude and temperature dependence. Our predicted N 2 O 2 vibrational relaxation times are noticeably shorter due to vibration-vibration transfer. For O 2 O we observe minimal temperature dependence. Our O 2 N and N 2 N predictions follow the M&W temperature trend at values roughly one order of magnitude smaller. For NO NO , N 2 O , NO N , and NO O we generate partial data due to currently incomplete PES sets. These first-principles-derived relaxation times are useful for informing relaxation models in gas-kinetic and fluid-dynamics simulations of high-enthalpy flows.


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    Title :

    Characteristic Vibrational and Rotational Relaxation Times for Air Species from First-Principles Calculations


    Contributors:

    Published in:

    Publication date :

    2025-04-01




    Type of media :

    Conference paper , Article (Journal)


    Type of material :

    Electronic Resource


    Language :

    English




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