Processes affecting the emission of the cathode zone plasma of a N 2 /Ti dc discharge were studied experimentally and theoretically. Light maxima occurring at the negative glow head (maximum II) are due to the electron-molecule excitation. Emission characteristics of this region, space distributions of lighting, dependence of the line intensity (I ) on the gas pressure (p) and current density (j d ) can be fully explained by the Monte Carlo (M-C) simulation of electron motion in this region. Emission characteristics of the space close to the cathode surface (maximum I) are complex, depending on the emitting species. Molecular lines are found to be emitted mostly due to the fast ion-N 2 interactions. The results of the analytical modelling of this process confirm the experimentally observed almost linear dependences of the intensities of these lines on the pressure and current density. Lines of atomic nitrogen are found to be due to the fast ion-N 2 interactions as well as to the fast ion-solid excitation, both accompanied by a dissociation. Particular attention was paid to the emission of sputtered material lighting in the space close to the cathode surface. This lighting results from the fast ion-sputtered atom interaction as well as from that of the sputtered atom with 'hot' atoms of the cathode surface layer. The experimentally observed dependences of the sputtered atom line intensity on the gas pressure (I ∼ 1/p) and the discharge current density (I ∼ j d × j d ) are qualitatively explained with a complex model that takes into account the analytical assessment of the energy distribution of bombarding ions, the M-C simulation of the ion-solid interaction and the M-C simulation of the motion of atoms roaming in the plasma phase. The plasma of the space close to the cathode surface (maximum I) of low-pressure discharges (∼0.1 Torr) is an effective light source for the optical emission spectroscopy of buffer gas and solid species.

Heavy particles bombarding the cathode surface in a glow discharge produce sputtering which liberates cathode material which then appears in the plasma phase in the vicinity of the cathode. The intensity of light emission from fundamental gas atoms depends linearly on the discharge current and this dependence can be explained if it is assumed that these intensities are proportional to the densities of the gas and electron current density. The electron/molecule excitation of sputtered material in the plasma phase is the main source of the light emitted by elements of the cathode. The intensity of light emission from this cathode material in the plasma depends parabolically on the discharge current density. This dependence can be explained if the intensity is assumed to be proportional to the densities of both the electron current and the stream of sputtered particles leaving the cathode surface. The density of the sputtered particles is in turn dependent on the energy of bombarding particles. The excitation of the sputtered material due to fast particle interaction with the cathode bulk seems to be a less important mechanism of light emission.

The energy spectrum of ions and fast neutrals generated in the cathode fall of a glow discharge is considered on the basis of the Davis model (1963) and in the light of the Boltzmann equation. A fundamental model based on the Boltzmann equation is developed and extended to include the effects of ionization processes due to electrons and ions and secondary electron emission from the cathode. It is shown that characteristic parameters associated with the model describing the spectrum can be easily obtained from relatively simple measurements of macroscopic properties of the glow discharge.

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