STUDIES OF NITROGEN AFTERGLOW .I. SURFACE CATALYTIC EFFICIENCY AND DIFFUSION-CONTROLLED DECAY OF ATOMIC NITROGEN

The temporal behavior of the afterglow light intensity in decaying nitrogen plasmas, as well as that of the number density of N+, N 2+, N3+, and N4 + ions, was studied in the pressure range of about 0.1 to 1.7 torr. The analysis of the light intensity decay curves resulted in a method of measuring the surface catalytic efficiency γN for the recombination of nitrogen atoms at the plasma boundary. The simultaneous identification of the ions present in the plasma by means of a quadrupole mass spectrometer ensures that the data relate to pure nitrogen as well as to extremely clean surfaces. The values obtained for γN of molybdenum sputtered on a glass surface decreased with pressure from a value of 0.22 at 0.09 torr to 0.04 at 1.35 torr. The studies also showed that part of the afterglow light emission is due to collisions between metastable nitrogen molecules which are produced in the afterglow by the atomic volume recombination process.