CN (B ²Σ⁺ → X ²Σ⁺) Violet System in a Cold Atmospheric-Pressure Argon Plasma Jet

Abstract

${\text{CN}} (B^{2}\Sigma ^{ + } \to X^{2}\Sigma ^{ + } )$ violet system was investigated using optical emission spectroscopy in a non-equilibrium microwave atmospheric-pressure plasma jet in argon expanding in air. From the analysis of the emission spectra of the discharge in the range of 380 and 400 nm, the violet system of CN was found to be overlapped with the ${\text{N}}_{2}^{ + } \left( {B^{2}\Sigma _{u}^{ + } , v = 1 \to X^{2}\Sigma _{g}^{ + } , v = 1} \right)$ and ${\text{N}}_{2} \left( {C^{3}\Pi _{u} \to B^{3}\Pi _{g} } \right)$ bands, sequence $\Delta \upsilon = - \;3$. A numerical disentangle technique, developed in this work, permitted to obtain a well resolved violet system from the different systems observed, namely the nitrogen First Negative and the Second Positive systems. The ${\text{CN}} (B^{2}\Sigma ^{ + } \to X^{2}\Sigma ^{ + } )$ band head intensity was determined and analysed as function of discharge powers between 30 and 150 W and fluxes between 2.5 and 10.0 slm. With aid of this numerical approach it was also possible to obtain the rotational temperature, from (1600 ± 100) to (2300 ± 100) K and vibrational temperature between (9000 ± 800) and (14,000 ± 800) K along the plasma jet. The kinetics of ${\text{CN}} (B^{2}\Sigma ^{ + } )$ state was analysed as well.