Role of Molecular Ions, Metastable Molecules, and Resonance Radiation in the Breakdown of Rare Gases

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Abstract
Theoretical calculations are made of the rates of arrival of atomic and molecular ions, of atomic and molecular metastables, and of nonresonance and resonance radiation at the cathode of parallel plane electrodes during the buildup of current preceding the breakdown of a rare gas. The electron density is assumed to increase exponentially with time and distance. Previous analyses are extended to obtain the particle currents of molecular ions and of metastable atoms and molecules at the cathode. The Holstein-Biberman formulation of the transport equation for the density of atoms in the resonance state is solved numerically to find the fraction of resonance photons arriving at the cathode. The fraction of resonance radiation reaching the cathode varies with the growth constant of the electron current in very nearly the same manner as for delayed photons and varies much less rapidly with electrode spacing and gas density than for the case of diffusing particles. The theory is applied to the calculation of the growth constant as a function of applied voltage for helium at 100 mm Hg pressure and a 1-centimeter gap. The growth of current is found to be controlled by the rates of arrival of molecular metastables, molecular ions, and resonance radiation at the cathode.