Spectroscopic study on rotational and vibrational temperature of N2 and N2+ in dual-frequency capacitively coupled plasma

Abstract

By using optical emission spectroscopy, the vibrational and rotational temperatures of N2 and N2+ in capacitively coupled plasma (CCP) discharges driven by dual-frequency 41MHz and 2MHz are investigated. The vibrational and rotational temperatures are measured based on the N2+ first negative system and N2 second positive system overlapped molecular emission optical spectrum, using the method of comparing the measured and calculated spectra with a least-square procedure. The influence of the rotational and vibrational temperatures with input power of the high frequency (HF) and low frequency (LF) as well as the gas pressure is discussed. It is found that the vibrational or rotational temperatures of N2 and N2+ are decoupled in dual-frequency CCP discharge. The influence of the LF power on N2+ rotational and vibrational temperature is much more than that of N2, while the influence of HF power is just opposite to the case of LF power. The reason for this is thought to be the variation of electron temperature when applying HF or LF power. Additionally, the increase of gas pressure makes the difference between the vibrational and rotational temperature decrease.

Progresses in Experimental Study of N2 Plasma Diagnostics by Optical Emission Spectroscopy

“…However, the rotational temperature of 1NS is higher than those of 1PS and 2PS, and consequently, it does not correspond to the translational temperature of neutral molecules. Similar results are reported on T R of 1NS of low-pressure discharge nitrogen plasmas (Huang et al, 2008). These experimental results possibly indicate that the dominant population process of excited states B 2 Σ u + of N 2 + is not the direct excitation from the ground state of neutral N 2 molecule, and not from excited states of neutral molecular state, either.…”

“…As for nitrogen ions, a number of papers reported that the first negative system (1NS), originated from B 2  u + state of N 2 + ion, shows higher rotational temperature than that from neutral molecules (e.g., Huang et al, 2008).…”

Spatiotemporal study of gas heating mechanisms in a radio-frequency electrothermal plasma micro-thruster

“…Simulated spectra are iteratively fitted to the experimental data to extract both vibrational temperature (T v ) and rotational temperature(T r ) using the same method as previously fully outlined in Greig et al [6]. At pressures of a few Torr, the collision frequency is sufficiently high to assume that the rotational and translational temperatures are in thermal equilibrium [15][16][17].…”

Neutral gas temperature estimates and metastable resonance energy transfer for argon-nitrogen discharges

“…18 The N þ 2 first negative system has been used to find gas temperature in a gliding arc discharge at atmospheric pressure, 13 a pulsed DC hollow cathode discharge, 19 and a low pressure dual frequency CCP. 20 The N 2 second positive system (C 3 P u ! B 3 P g ) is the most common band used, with gas temperature estimates made for capacitively coupled and inductively coupled plasma discharges, 5,10,[20][21][22] a radio-frequency (RF) helicon discharge, 23 and low pressure glow or positive column discharges.…”

“…20 The N 2 second positive system (C 3 P u ! B 3 P g ) is the most common band used, with gas temperature estimates made for capacitively coupled and inductively coupled plasma discharges, 5,10,[20][21][22] a radio-frequency (RF) helicon discharge, 23 and low pressure glow or positive column discharges. 24,25 Temperatures of higher pressure and atmospheric pressure discharges have also been analysed with the N 2 second positive system, 4,26,27 and also temperatures during the first 400 ns of spark breakdown for an N 2 discharge.…”