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

Abstract

We have generated a N2 flowing discharge sustained by surface waves employing a 2.45 GHz high frequency source. The N2 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(2p3 4S0) absolute density was measured in the discharge by actinometry. We have introduced the effect of the N2(X1 Σg+) 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 4S0) by N2(X1 Σg+, v) states. The 811.5 nm Ar and 821.6 nm N lines, from 2p9 → 1s5 and 3p 4P0 → 3s 4P 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(2p3 4S0) absolute density in that region. The extinction point of the 580.4 nm band of the N2 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(2p3 4S0) absolute density values as a function of power and pressure only by application of OES techniques. Moreover, we demonstrate here that the N(3p 4P0) state is quenched by N2(X1 Σg+, v ⩾ 2) molecules forming N2(b 1Πu, v = 0) and N(4S) states, in agreement with Catherinot and Sy.