Nitrogen ion dynamics in low-pressure nitrogen plasma and plasma sheath

Laser-induced fluorescence (LIF) excitation and time-resolved LIF spectroscopy have been used to explore the interaction of a nitrogen plasma with a metal surface. The rotational temperature, the concentration of N+2, and the lifetime of N+2(B2Σ+u)υ=0 were measured as a function of distance from the metal surface. It was observed that the lifetime of the excited ion decreases sharply in the plasma sheath which is created in front of the metal surface. The concentration of N+2(X 2Σ+g), which was measured simultaneously with the lifetime of excited N+2, indicates a quasilinear decrease from the cathode to the grounded surface. Trot undergoes a gradual reduction from the bulk plasma up to the surface where its value is a good approximation of the surface temperature. An interpretation of these phenomena including a numerical simulation of the lifetime decrease is proposed here. The calculated values are in good agreement with experimental results. The dependence of lifetime decrease on the sheath potential as well as on other important parameters (cross section, profile of the electric field) is further discussed.