Experimental and theoretical study of dissociation in the positive column of a hydrogen glow discharge

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Abstract
The positive column of a hydrogen glow discharge was studied under typical operating conditions: gas pressure from 0.3 up to 5.0 Torr and discharge current from 1 up to 50 mA. Optical emission spectroscopy, optical absorption spectroscopy, and laser induced fluorescence have been employed in order to determine the gas temperature (300<Tg<600 K), the density of ground state hydrogen atoms (1012<[H(1s)]<1013 cm−3), and the kinetic temperature of H atoms (336<Ta<1600 K), respectively. Langmuir probes were utilized to measure the electric field (8<E<61 V cm−1) in the positive column. A kinetic model based on the solutions to the homogeneous electron Boltzmann equation coupled to a set of rate balance equations for the vibrational levels H2(X 1Σg+,v), H atoms, and H− ions was developed in order to predict the concentrations of these species. From a comparison between the measured and calculated concentrations of H atoms, the reassociation probability on the wall, in Pyrex glass, is estimated to be ≅10−2.