Measurements of N(⁴S) absolute density in a 2.45 GHz surface wave discharge by optical emission spectroscopy

We have generated a N 2 flowing discharge sustained by surface waves employing a 2.45 GHz high frequency source. The N 2 dissociation was studied in the discharge and post-discharge regions by optical emission spectroscopy (OES) as a function of the experimental parameters: discharge power (30–160 W) and absolute pressure (1–20 Torr), at 0.5 Slm −1 flow rate. The N(2p 3 4 S 0 ) absolute density was measured in the discharge by actinometry. We have introduced the effect of the N 2 ( X 1 Σ g + ) vibrational temperature in the actinometry equation. Such a consideration was made based on the work of Catherinot and Sy (1979 Phys. Rev. A 20 1511) which presents a profound discussion about the quenching mechanism of the N(3p 4 S 0 ) by N 2 ( X 1 Σ g + , v ) states. The 811.5 nm Ar and 821.6 nm N lines, from 2p 9 → 1s 5 and 3p 4 P 0 → 3s 4 P transitions have been utilized here. Both are easily observed in the surface wave discharge. Further, the NO chemical titration was carried out in the late post-discharge furnishing the N(2p 3 4 S 0 ) absolute density in that region. The extinction point of the 580.4 nm band of the N 2 1st positive system was measured. The density values obtained by actinometry are validated by comparison with those measured in the post-discharge region. The two sets of data, function of pressure and discharge power, may be related by the mass conservation equation. The work provides the experimental N(2p 3 4 S 0 ) absolute density values as a function of power and pressure only by application of OES techniques. Moreover, we demonstrate here that the N(3p 4 P 0 ) state is quenched by N 2 ( X 1 Σ g + , v ⩾ 2) molecules forming N 2 ( b 1 Π u , v = 0) and N( 4 S) states, in agreement with Catherinot and Sy.