Spatial profiles of fundamental properties for the moderate power (500 W) helium microwave induced plasma (MIP) have been obtained and the character of the plasma was carefully studied. Excitation (He and Fe), ionization and rotational temperatures of some molecular species (OH and N+2) show large differences among themselves, ranging from 2130 to 5890 K. The measured electron number density was 2.3 × 1014cm-3. The differences in temperatures are greater than those reported for other Ar or N2plasmas. Apparent overpopulation of higher energy levels in OH and N+2suggests the existence of high energy species, probably electrons, in the plasma. The rotational temperature increases moderately for this plasma compared to those operated at lower power, but it is still not sufficiently robust to allow easy introduction of aqueous samples. The plasma approaches equilibrium more closely at the top owing to the collisional relaxation. © 1994.
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