Origin of temperature discrepancy between DFCS rotational and Pitot translational measurements in USF

Determine the physical origin of the discrepancy between the rotational temperature of OCS inferred from direct frequency comb spectroscopy (approximately 49.5 K by contour fit and 48.9 K by Boltzmann plot) and the translational temperature derived from Pitot impact pressure measurements (approximately 32 K) in the uniform supersonic flow generated by Nozzle 9 with argon buffer gas in the HILTRAC apparatus, including assessment of possible boundary-layer effects, collisional broadening contributions, and measurement assumptions.

Background

In their DFCS measurements of OCS, the authors derive rotational temperatures around 49–50 K, while independent Pitot impact pressure measurements indicate a translational temperature of ~32 K for the same flow and nozzle configuration.

They consider potential factors such as boundary layer effects and collisional broadening but find no systematic evidence in residuals or Boltzmann plots necessitating multiple temperatures, leaving the discrepancy unexplained.