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Progress in Plasma Processing of Materials, 1997

ISBN:
1-56700-093-2 (Print)

SPECIFIC PROBLEMS OF ROTATIONAL TEMPERATURE DETERMINATION IN PLASMAS OF MOLECULAR GASES

Spyros Stamou
Plasma Chemistry Department of Chemical Engineering, University of Patras P.O.Box 1407, 26500, Patras, Greece

Nikos Spiliopoulos
Laboratory of Plasma Chemistry Department of Chemical Engineering, University of Patras P.O. Box 1407,26500 Patras, Greece

Dimitris Mataras
Plasma Technology Laboratory -Dept. of Chem. Engineering-University of Patras, P.O.Box 1407, 26500 Patra, Greece

Dimitrious E. Rapakoulias
Plasma Technology Lab, Dept. Chem. Engineering, University of Patras, P.O.Box 1407, 26500 Patra, Greece

Abstract

The rotational temperature of the Á2Δ excited state of SiH has been determined in a silane r.f. glow-discharge by optical emission spectroscopy, using both the Boltzmann diagram method and a detailed simulation of the emission spectrum utilising a least squares fitting (LSF) method. It is shown here that the LSF is much more reliable and a careful use can lead to accurate results. For this, an improved term value formula and an optimisation of the set of constants are used to calculate the best possible simulation of the spectrum. The Boltzmann diagram results in a rotational temperature of 2900 ± 200 K while the LSF method gives 2840 ± 50 K. In both methods the experimentally determined FWHM of the optical system is of major importance. Finally, deviation of the observed Λ-splitting from the calculated values is observed and unequal Λ-doublet populations are detected in some cases.