Studies Of Reactive Species In Low Temperature Plasmas By Laser Induced Fluorescence Spectroscopy And Mass Spectrometry

The reactive species diagnosis of low temperature plasmas plays a very important role in many respects including the investigation of plasma reaction mechanism, the deep understanding of plasma physical chemistry processes, the optimization of plasma reactor and the development of corresponding plasma processing technique. The realization of the reactive species diagnosis is very difficult and challenging in plasma diagnosis research field. In this dissertation, the following works have been performed:â… . The study of nitrogen metastable state N2(A3∑ll+) in high pressure nanosecond pulsed DC discharge plasma1. The laser induced fluorescence plasma diagnostic apparatus (LIFPDA) has been established and the suppression of laser stray light, the design of discharge chamber as well as optimization of fluorescence collection system have been described in detail. The instrument control and data acquisition system have been developed and programmed based on Lab VIEW platform to realize the remote control of the dye laser system and the monochromator, the synchronous data acquisition by the oscilloscope, on-line data precessing and storage function. The results have indicated that, this diagnostic system has a great development potential, which can be used for the (ro-) vibrational resolved investigation of the transient reactive species in discharge plasma and provide the automatic platform and foundation for developing the complex laser spectroscopy plasma diagnostic technique.2. The metastable state N2(A3∑u, v=0) in the nanosecond pulsed DC discharge plasma with point-point electrode structure has been investigated in a temporally and spatially resolved manner using LIFPDA system. The invesitigation has been concentrated on the density evolution dependence of N2(A3∑u+,v=0) in the postdischarge on the parameters such as discharge pressure and the composition of discharge gas. The results indicate that the density distribution of N2(A3∑u+,v=0) is nearly uniform along the discharge gap. And a fast quenching process of N2(A3∑u+,v=0) exists in the very early stage of afterglow and especially dominant near the anode, according to the results, the N(4S) atoms should play an important role during the quenching process of N2(A3∑u+,v=0). It seems that this fast quenching behavior of N2(A3∑u+,v=0) can be ascribed to the interplay between pooling reaction and collisions with N(4S) atoms through N2(A3∑u+)+N2(A3∑u+)â†'N2*N2and N2(A3∑u+)+N(4S)â†'N(2P)+N2respectively. Meanwhile, the addition of O2has speed up the decay process of N2(A3∑u+,v=0), this has proven the fact that O2is the quencher of nitrogen metastable and can accelerate the deactivation of nitrogen metastable. The experiment results provide the new data to the understanding of the generation of reactive species and quenching process in high pressure nanosecond pulsed discharge plasma.â…¡. The neutral species distribution measurement in C2H2/He discharge plasma by laser ionization mass spectroscopyThe non-resonant laser ionization mass spectrometry has been used to measure the distribution of neutral species in C2H2/He pulsed discharge plasma. The preliminary results have been discussed. The experimental results indicate that the intermediate species with an even number of carbon atoms are dominant in C2H2plasma and the production of most of species with odd number of carbon atoms are suppressed. The most prevalent neutral species identified are C4H2, C5H5, C6H3and C6H5, while the diacetylene molecule C4H2is the most dominant neutral hydrocarbon product of C2H2plasma. The addition of Ar to the discharge gas had a significant influence in the detected species in our discharge apparatus. Some species that haven’t been detected in the previous measurement were observed such as C2, C2H4. The experiment has been proven that the laser ionization time-of-flight mass spectrometry technique can be applied for the netrual species detection, and has great development potential compared with traditional threshold ionization mass spectrometry. This work is the preparatory work to accumulate experience and hardware foundation for the subsequent establishment of the diagnostic system that combined resontant multiphoton ionization technique with mass spectrometry, in order to realize the (ro-)vibrational resolved diagnosis of reactive species.