The production and loss ofN 2 + ions in the nitrogen afterglow

Abstract

The time dependence of the number density of nitrogen ions was studied in the pressure range of about 0.1 to 1.7 Torr by means of mass spectrometric probing of decaying nitrogen plasmas. The analysis of theN 2 + decay curves showed thatN 2 + ions are produced in the afterglow by collisions between metastable nitrogen molecules. Energy level and radiative lifetime considerations indicate that one of the metastable molecules is in thea′ 1∑ u } state, while the other metastable molecule may be in the same state or in theA 3∑ u + or3 Δ u state. The surface catalytic efficiency for de-excitation of the metastable molecules involved upon striking the molybdenum covered plasma container walls was estimated to be smaller than 2×10−3 at a pressure of 0.09 Torr. If both interacting metastable molecules are in the a′1 bE u } state the measurements result in a value of 1.3×10−18 cm2 for the cross section for destruction of this state by collisions with ground state nitrogen molecules.