Molecular dissociation in N₂–H₂ microwave discharges

A microwave N 2 –H 2 discharge driven by a travelling surface wave is investigated as a source of ground state N( 4 S) and H(1s) atoms. Experimental investigations have been carried out in a plasma source operating at 2.45 GHz at low-pressure conditions ( p = 0.5–2 Torr). By means of optical emission spectroscopy and probe diagnostic techniques, the population densities of ground state atoms have been detected. The dissociation kinetics is discussed in the framework of a theoretical model based on a self-consistent treatment of the main discharge balances, wave electrodynamics and plasma–wall interactions. Electron–ion surface recombination processes involving and ions are the most important sources of N( 4 S) gas phase atoms for the conditions considered. The relative number of N( 4 S) atoms in respect to the total neutral density remains approximately constant for percentages of H 2 between 10% and 50% at nearly constant electron density. The competitive interplay of two important source channels of H(1s) atoms, namely electron impact dissociation of H 2 and H 2 dissociation via the quenching of nitrogen and metastables, determines a smooth decrease of hydrogen dissociation when the amount of hydrogen increases up to 50% in the mixture.