Observation of ¹D−¹S forbidden optical emission of atomic oxygen in atmospheric‐pressure N₂/O₂ plasma jet

Abstract

We observed green optical emission from an atmospheric-pressure N 2 /O 2 plasma jet. The green optical emission was composed of a line emission at λ = 557.71 ± 0.03 nm and a broadband component at 530 ≤ λ ≤ 560 nm. The line emission was assigned to the 1 D− 1 S forbidden transition of atomic oxygen, whereas the broadband emission was due to the formation of O(1 S)N 2 excimer. We measured the absolute densities of O(1 S) and O(1 S)N 2 using a spectrograph with the absolute sensitivity calibration, and we discussed the kinetics in the green plasma jet on the basis of the absolute O(1 S) and O(1 S)N 2 densities. According to the rate coefficients and the transition probabilities reported in literature, the present experimental results are explained if the densities of N 2 (A 3 Σ + u) and O(3 P) are 9 × 10 13 and 3 × 10 13 cm −3 , respectively.

Characteristics of the O(1S) to O(1D) 557.7 nm green emission observed in an argon plasma jet

“…In other words, the 557.7 nm emission that occurs in one voltage period reflects the O( 1 S) and ArO( 1 S) excimers generated in the previous few periods. This characteristic of the green afterglow is similar to the phenomena in nitrogen discharges where the spatial afterglow is sustained by the transport of long-lived species [13,42,43].…”

“…In addition, the excimers formed by the O( 1 S) atoms with foreign species such as N 2 or Ar can make this forbidden transition probability much larger, which might gain from the collision-induced emission [5,10]. That is why, in recent years, researchers observed the 557.7 nm line in dielectric barrier discharges (DBDs) at atmospheric pressure with N 2 (or N 2 + O 2 ) as the working gas [11][12][13] or in Ar plasma jets [14], even though the emission intensities were either too faint to be seen by the eye or the green plasma plumes were very short.…”

Characterization of an atmospheric pressure plasma jet producing the auroral transition O(1S) to O(1D)

“…Recent work demonstrated a clear signal of the O( 1 S)−O( 1 D) transition along with detection of ON 2 excimers based on the spectral lineshape [18,24,25]. A set of reactions to create O( 1 S) has been discussed previously [10,26,27] that first relies on the creation of metastable nitrogen (N 2 A 3 Σ + u ). This framework may not be accurate for argon plasmas where the only N 2 is due to the surrounding atmosphere [24].…”

On the green aurora emission of Ar atmospheric pressure plasma

“…Recently, researchers observed green aurora line of wavelength 557.7 nm produced by atmospheric pressure plasma [14][15][16][17][18][19][20]. Several early works reported the observation of the aurora line emission from atmospheric pressure DBD with N 2 or its mixtures as working gas [14,15,20].…”

“…However, as the emission intensity of the aurora line is weaker than N 2 or NO emission, the green aurora emission is not obvious by naked eyes. Then, Sasaki et al reported visible green aurora emission from atmospheric pressure plasma jet (APPJ) with N 2 +O 2 (7 slm+50 sccm) as working gas [16]. Sylvain Iséni reported weak green aurora emission in their Ar APPJ [17].…”