Behaviour of N2 Active Species in Microwave Plasma and Early Afterglows at Low Pressure | Chapter 9 | Plasmas Afterglows with N2 for Surface Treatments synthesis 2024

The excited states in N₂ plasma and flowing afterglows at reduced pressure are studied for the plasmas and for the afterglows. The N₂ flowing microwave discharges have been investigated by emission spectroscopy in the following conditions:  N₂ at p = 5 Torr, flow rate of 0.3 slpm, t = 1.5×10^-3 s and microwave power of P = 150 W.

Two experimental setups were analyzed: one with the plasma (produced inside a 5 mm ext. dia. tube) directly connected to a larger post-discharge tube (with a diameter of 15 mm) and another with the introduction of an Ar-NO_ext mixture after the plasma in the small tube.

Under these conditions, the production of N₂+ ions in the plasma and in the early afterglow is done predominantly by electron collisions. After the end of the plasma up to the pink afterglow, N₂(A) and N₂(X,v>11) were the excited species at the origin of the N₂(C) and N₂+(B) emissions. A self-consistent theoretical model was introduced to explain the production of the N₂ active species by particle kinetics.

The intensity ratio I_{\(N_2^+(B)\)}/I_{\(N_2(C)\)} increased 15 times from the plasma to the pink afterglow. In this setup, the gas temperature was about 1000 K in the plasma and 700 K in the pink afterglow. In a second setup, the plasma end was at 12 cm of the post-discharge tube. The gas temperature was lower: 750 K at 2 cm and 400 K at the plasma end (3.5 cm). The effect of adding an Ar-NO_ext gas mixture (used for N-atom titration in the late afterglow inside the 15 mm diameter tube) at the discharge end was studied along the 5 mm diameter tube. It was concluded first that the destruction of N-atoms by NO_ext decreased the intensity of the N(²P) and N₂(B) radiative states. Second, the electrons at the plasma end could excite the N₂(C) and N₂+(B) radiative states. It was revealed that the destruction of N-atoms caused by the addition of NO_ext also produced a decrease in the intensities of the N(⁴P) and N₂(B) radiative states. The plasma electrons were still influential in the excitation of the N₂(C) and N₂+(B) radiative states after the plasma end.

 

Author (s) Details

Julio Henriques
Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, 1049-001, Lisbon, Portugal.

 

André Ricard
LAPLACE, Université de Toulouse, CNRS, INPT, UPS, 118 route de Narbonne, 31062 Toulouse Cedex 9, France.

 

Please see the book here:- https://doi.org/10.9734/bpi/mono/978-93-49473-93-5/CH9