Fundamental studies of an atmospheric-pressure microwave plasma sustained in nitrogen for atomic emission spectrometry

We report the results of fundamental studies of an atmospheric-pressure microwave plasma sustained in nitrogen. Plasma composition was modelled using chemical equilibrium software, with the measured temperature used as input for the program. The modelled electron density agreed well with the electron density measured in Thomson scattering experiments. The various temperatures measured (electronic excitation, electron, and rotational) were comparable, and we argue that the N-2 microwave plasma is close to local thermodynamic equilibrium (LTE). This close-to-LTE behaviour was used as a basis to calculate the emission spectra of selected elements; the calculated spectra were compared with measured library spectra, and good agreement was found.