Spectroscopic Temperatures of a Moderate-Power Argon Microwave-Induced Plasma

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Abstract
The present study reports rotational and excitation temperatures for a moderate-power Ar microwave-induced plasma (MIP) operating at 500 W forward power and zero W reflected power (as measured at the generator). We report rotational and excitation temperatures as a function of position in the plasma using both axial and lateral viewing modes with, and without, solution nebulization. For the sake of comparison, rotational temperatures ( Trot) were determined both by the fundamental, or slope, method and by the isointensity method as described by Dieke and Crosswhite (see text for references). A discussion of rotational state distributions as they are related to local thermodynamic equilibrium and rotational temperature determinations is included. In determining Trot the principal spectral region of interest is the well-known 3064 Å band characteristic of OH radical. With the use of isointensity method of calculation the temperature in the central region of this plasma was determined to be 3580 K. The excitation temperature ( Texc) was determined by the “slope” method with the use of the Ar plasma support gas excited-state emission lines. The excitation temperature at the center of this Ar MIP was found to be approximately 14,200 K by this method. These values for Trot and Texc suggest that this plasma is more thermal than those MIPs of low power.