Inferring gas temperature from N₂ emission via rotational distribution of the N₂ B³Π_g and C³Π_u states

Abstract

Optical Emission Spectroscopy (OES) has been frequently used to measure the rotational temperature of a plasma. The technique is relatively simple to implement and non-intrusive. However, in the visible and ultraviolet spectral regions, it relies on emission from excited vibronic states whose rotational and vibrational temperatures might not be equilibrated with the bulk temperature of the plasma. Oftentimes, rapid equilibration between the rotational and translational modes occurs so that these temperatures are equilibrated. However, many cases exist where these modes are not equilibrated. In this work, we have developed a simple model that can be used as an experimental tool when using OES. This model helps identify whether equilibration between rotational and translational modes is expected. In cases where non-equilibrium is expected, the model may be used to provide an estimate of the bulk gas temperature. An illustrative example is given where we use this model to analyze previous measurements made in a thermal nonequilibrium discharge.