Spectroscopic Method for Determination of N2(A3 Σu) Metastable Density in Atmospheric Pressure Non-Equilibrium N2 Plasmas

Summary form only given. N
₂
meta-stable species such as N
₂
(A
³
Σ
_u
) are very important in plasma treatments because of their high-energy contents, which make plasmas more sustainable and chemically reactive. However, direct measurements of these meta-stable species are not easy. In this study, a spectroscopic method to determine the N
₂
metastable density has been developed by using a simple collisional-radiative model (CR model) with several molecule-molecule reactions included. The N
₂
(A
³
Σ
_u
) metastable density can be calculated from the density ratio of N
₂
(C
³
Π
_u
)/N
₂
(B
³
Π
_g
) by using the CR model. Governing equations for the model have some terms related to molecule-molecule reactions that depend on vibrational temperatures, which can be determined from the measured spectrum of N
₂
second positive system by comparing with the simulated spectra. In addition, the density ratio of N
₂
(C
³
Π
_u
)/N
₂
(B
³
Π
_g
) can be evaluated from the emission intensity ratio of N
₂
second positive system/N
₂
first negative system. By measuring these spectra, the N
₂
metastable density is successfully determined through both the vibrational temperature and the density ratio of N
₂
(C
³
Π
_u
)/N
₂
(B
³
Π
_g
) without knowing electron temperature and electron density