Optical emission spectroscopy, thermodynamical and thermal disequilibrium aspects in an inductively coupled plasma torch. Experimental applications to N-2-O-2 mixtures

The purpose of this article is to study experimentally and theoretically th e spectral line ratios O 700.22 nm/N 746.87 nm with a sample gas mixture of N-2 and O-2 (notably for pure air) in an inductively coupled plasma (ICP) torch. We study theoretically the influence of the thermal disequilibrium on the c omposition and on the volumic enthalpy in a plasma produced in an ICP torch , and we show that the lower temperature in the plasma is set by the power supplied by the inductive coil. If the temperature (or heavy species temper ature for plasma out of thermal equilibrium) is sufficiently low (<5000 K), we show that the thermal disequilibrium has no influence on intensity spec tral line ratios (O 700.22 nm/N 746.87 nm). We compare these results with t hose obtained experimentally in the case of N-2-O-2 mixtures, and we show t hat the determination of monatomic spectral line ratios (O 700.22 nm/N 746. 87 nm) solely depends on the initial sample gas composition introduced in t he ICP torch.