Emission spectroscopy of molecular low pressure plasmas

The diagnostic tool of optical emission spectroscopy with applications to molecular low pressure plasmas is introduced and the underlying principles for the analysis of molecular radiation are summarized. Results for rotational, vibrational and electronic population densities in electronically excited states and in the ground state of diatomic molecules such as hydrogen and nitrogen are shown. Besides molecular densities atomic densities are obtained and the relevance of opacity of resonance lines in the analysis is discussed. In more complex plasmas such as hydrocarbon plasmas, the radiation of radicals is used to determine particle densities. Here, the contribution of the dissociative excitation mechanism has to be taken into account. A simple monitoring tool for the determination of particle density ratios is emphasized based on the measurement of intensity ratios. Results are presented for plasma applications with volume processes as well as with plasma surface interaction.