Molecular ion and metastable atom formations and their effects of the electron temperature in medium-pressure rare-gas positive-column plasmas

A theoretical study has been made of the medium-pressure rare-gas positive-column plasma by taking into account the effects of molecular ion formation, volume recombination and ionisation due to metastable atoms, simultaneously. Calculated values of the electron temperature and the densities of metastable atoms, molecular and atomic ions, at various gas pressures for both He and Ne gases are presented. Numerical results show that in a rare-gas positive-column plasma, molecular ions become dominant in the discharge as the gas pressure increases above approximately 10 Torr. Theoretical values are compared with the experimental data and discussed. A new method to determine the three-body conversion rate coefficient is also proposed. (author)