Determination of gas temperature in an open-air atmospheric pressure plasma torch from resolved plasma emission

The resolved emission spectrum of an open-air atmospheric pressure plasma torch was recorded with a 0.5 m spectrometer and CCD camera. The plasma emission under these conditions was found to be dominated by continuum radiation and emission from species, which obscured large portions of the N-2 second positive emission spectrum. Despite these difficulties, the gas temperature of the torch could be determined from a fit of partially resolved N-2(+) first negative vibrational transitions and a blackbody fit to the continuum radiation. The vibrational temperature, determined from a Boltzmann plot, was 4300+/-900 K while the blackbody radiation temperature was 4400+/-400 K. To check these gas temperature determinations, measured spectra over selected spectral regions were compared with spectral simulations using N-2(+) first negative emission, N-2 second positive emission, and a blackbody. Best agreement between measured and simulated spectra was with blackbody temperature, rotational temperature, and vibrational temperature set to 4400 K. (C) 2003 American Institute of Physics.