Mass Spectrometric Studies of Metastable Nitrogen Atoms and Molecules in Active Nitrogen

Abstract

Metastable nitrogen atoms and molecules produced by electrical discharges in N2 and He–N2 mixtures have been studied by mass spectrometry. N(2D) and N(2P) atoms in addition to ground-state N(4S) atoms were clearly identified in the products observed about 1 msec after leaving the discharge. The concentration of metastables was much higher for a discharge in a He–N2 mixture than for a discharge in pure N2. Assuming that the ionization cross sections for the atoms at corresponding excess energies were equal, the relative concentrations were: N(4S) = 1.00, N(2D) = 0.17, and N(2P) = 0.06 for the He–N2 discharge; and N(4S) = 1.00, N(2D) = 0.0068, and N(2P) = 0.0025 for the pure-N2 discharge. Metastable N2 molecules with excitation energies of up to several eV were also observed. Ionization processes involving the metastable molecules are discussed. To explain the experimentally obtained N2 ionization curves, it was found necessary to assume that, in addition to vibrationally excited ground-state molecules, an appreciable concentration of N2 molecules in various vibrational levels of the metastable A3Σu+ state were present. Metastable N atoms are very easily deactivated by wall collisions. Metastable molecules survive for longer times, indicating that they are less readily destroyed by wall collisions.