Cross section for disalignment of excited neon atoms due to neon or helium atom collisions

Abstract

In a positive column plasma of glow discharge in neon the population of metastable atoms ( configuration) is substantial. Linearly polarized pulsed laser light excited these atoms to one of the configuration levels, and the direct fluorescence was observed with its polarized components resolved. From the temporal development of the intensities of these components, the disalignment (depolarization) rate due to atom (neon or helium) collisions was determined. From its atom-density dependence the rate coefficient was determined, and from the temperature (42-650 K) dependence of the rate coefficient, the disalignment collision cross section was estimated as a function of energy in the energy range of the order of 10 meV. The cross section of the (Paschen notation) atoms has positive dependence on energy, while that of the atoms has a negative dependence. The cross sections thus determined serve as a quantitative test of the molecular potentials to the order of . In order to confirm that the temperature of the metastable atoms in the plasma is equal to the temperature of the surrounding wall, an additional experiment was performed; the line profile of the CW laser-induced fluorescence was observed for a plasma at liquid nitrogen temperature, and the metastable atom temperature was found to be 78 K.