UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS

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Conference: Bucharest University Faculty of Physics 2003 Meeting


Section: Optics, Spectroscopy, Plasma and Lasers


Title:
Computer simulation of molecular nitrogen emission spectral systems. Application to study of rotovibrational temperatures of high pressure RF expanding plasma


Authors:
D. Crintea, C. Petcu, A. Lazea, S. Vizireanu, B. Mitu, G. Dinescu*


Affiliation:
National Institute for Laser, Plasma and Radiation Physics,

POBox MG 36-Magurele, Bucharest, 76900 Romania, *e-mail: dinescug@alpha1.infim.ro


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Keywords:


Abstract:
Due to its simple operation the optical emission spectroscopy (OES) is largely spread as diagnostics technique, in spite of the fact that quantitative results are derived with difficulty. The information provided concerns species identification and, in the frame of assumed plausible models, plasma and species densities and temperatures. In addition, computer aided diagnostics, based on simulation of emitted spectra, is a powerful tool which allows temperatures evaluation even in the case of use of less expensive low resolution equipment. In this contribution we present results regarding the computer generation of the N2 (C3ƒŽu ¨ B3ƒŽg), 2nd positive (SPS) and N2+ (B2ƒ°+u ¨ X2ƒ°+g) 1st negative (FNS) molecular nitrogen spectral systems. First the basic of the method is described, and the role of every step in calculating the spectra is discussed. Secondly, the structure of the numerical code is explained. The program is provided with a friendly interface, making it easy to be handled even by inexperienced users. We have used the program aiming to study the new high pressure expanding plasma, working up to atmospheric pressure, which has been developed in our laboratory. The spectral behavior of this plasma was studied with a spectroscopic setup consisting of a focusing lens, optical fiber, grating monochromator (SPM 2), photomultiplier, and acquisition card. The above-mentioned spectral systems of nitrogen were recorded in various plasma conditions: electrode geometry, pressure and RF power, and position in expansion. The rotational and vibrational temperatures were determined by fitting the acquired SPS spectra with simulated ones. The decrease and convergence of rotational and vibrational temperatures to a similar value with increasing pressure proves the role of increasing collisional rate in equilibration of plasma subsystems.