THE EXCITED-STATE POPULATION-DISTRIBUTION OF TITANIUM ATOMS IN A DC ARGON PLASMA-JET AT ATMOSPHERIC-PRESSURE

The distribution of excited-state titanium atoms in an argon plasma at atmospheric pressure has been studied by spectroscopic measurements. The upper levels of the argon atoms were found to be in equilibrium with the continuum; electron collisions are dominant for these levels and the Boltzmann temperature compared favorably with the LTE temperature obtained from the extrapolated electron density. The distribution of titanium atoms was found to be far from equilibrium. The temperature determined from the intensity ratios of titanium emission lines differs by a factor of more than two from the electron temperature obtained from argon emission-line data. The titanium data were corrected by using a modified diffusion model. The resulting electron temperature is within 14% of that determined from a Boltzmann plot of the argon emission lines. This study suggest a procedural method to use emission-line data of metal atoms in a low-temperature plasma to obtain a better estimate of the electron temperature and to predict other population densities for situations in which the energy separation of the excited state from the ionization level is sufficiently large so that radiation processes are dominant over excited-state depopulations.