Gas-surface-interaction measured by spectroscopy methods

The interaction of N₂- and NO-molecules of high kinetic energy colliding with a solid wall is investigated by two spectroscopic methods: laser induced fluorescence (LIF) and electron beam fluorescence (EBF). They allow one to measure the population of rotational levels of the molecules, which is necessary to define the rotational temperatures of the incoming (undisturbed) and the reflected (coming back from the wall) molecules. Using pure test gases N₂ or NO or NO/N₂ mixtures provides flow velocities from 800 to 1500 m/s in a supersonic free jet expansion; seeding with light gas like He accelerates the flowing molecules up to 3000 m/s. The experimental results show a strong influence of the kinetic energy of the incoming flow, a minor influence of the wall temperature, a minor influence of the wall materials except for the combination NO on Pt, and an influence of the Knudsen number except for the free molecular conditions