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 510^-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 ({N₂}^+) = (2. 90. 3) 10^-7 cm^3/sec. The variation of the metastable decay rate with nitrogen pressure gives a cross section of (5. 41. 0) 10^-16 cm^2 for the de-excitation of the ^3P₂ neon-metastable state by nitrogen molecules. At higher nitrogen pressures and shorter discharge pulse lengths (25-50) the recombination controlled afterglows are dominated by N₄^+ ions, the resulting recombination coefficient being approximately 210^-6 cm^3/sec. All values refer to a temperature of 300^.