Electron-Ion Recombination in Nitrogen

Combined microwave, mass spectrometric, and optical techniques have been used to study the afterglow decay of electrons, ions, and excited atoms from microwave discharges in nitrogen-neon gas mixtures under conditions where N₂⁺ is the only significant afterglow ion, i.e., at nitrogen pressures less than 5×{}10^-3 Torr. Optical absorption studies show that neon-metastable atoms, an undesirable ionization source, are present in the afterglow, the concentration being inversely related to the discharge pulse length. Under conditions of no detectable metastable-atom concentration and for neon pressures in the range 15 to 30 Torr, the afterglow decay is controlled by the recombination of N₂⁺ ions and electrons, yielding a recombination coefficient α(N₂⁺)=(2.9±0.3)×10^-7 cm³/sec. The variation of the metastable decay rate with nitrogen pressure gives a cross section of (5.4±{}1.0)×{}10^-16 cm² for the de-excitation of the ³P₂ neon-metastable state by nitrogen molecules. At higher nitrogen pressures and shorter discharge pulse lengths (25-50 {μ}sec) the recombination controlled afterglows are dominated by N₄⁺ ions, the resulting recombination coefficient being approximately 2×{}10^-6 cm³/sec. All values refer to a temperature of 300^∘{}K.