Spectroscopic Observations on Induction-Coupled Plasma Flames in Air and Argon

Publisher Website
Google Scholar
Abstract
Plasma flames in argon and air have been maintained at atmospheric pressure by rf induction in a 100-mm-wide quartz tube for extended times with only forced air required for tube cooling. For air, a rotational temperature of 6300°K at the central point of the induction zone was determined from intensity ratios of both sextet components and unresolved sextets in the 0, 0 band of the N2(2+) system. Absolute intensity measurements in this band and in the 0, 0 band of the N2+(1−) system yielded probabilities of 1.34×107 sec−1±14% for the C 3πu→B 3πg transition and 1.15×107 sec−1±14% for the B 2Σu+→X 2Σg+ transition, which agree well with values in the literature. Under the assumption of local thermal equilibrium (LTE) in the plasma, radial temperature distributions at the coil midsection were derived for both systems. Results agree within 7%, which supports the validity of the above values for transition probabilities and indicates that deviations from LTE are less than 10%. Average electron densities were determined for argon and air at the coil midsection from Stark broadening of the Hβ line. For air a value of 5×1014 cm−3 has been found which is slightly above the equilibrium value. The value for argon is 1.7×1015 cm−3. It correlates well with data from other sources which indicate that the average electron density in argon is inversely proportional to the tube radius.