We present molecular-scale computational rotational-vibrational relaxation studies for , , and . 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 , , and 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 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 vibrational relaxation times are noticeably shorter due to vibration-vibration transfer. For we observe minimal temperature dependence. Our and predictions follow the M&W temperature trend at values roughly one order of magnitude smaller. For , , , and 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.
Characteristic Vibrational and Rotational Relaxation Times for Air Species from First-Principles Calculations
Journal of Thermophysics and Heat Transfer ; 39 , 2 ; 223-249
2025-04-01
Conference paper , Article (Journal)
Electronic Resource
English
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