Emission Spectroscopy of the Cathode Fall Region of an Analytical Glow Discharge

Abstract

Stark spectroscopy of hydrogen Balmer lines and neutral helium lines with forbidden components is used for the study of an analytical glow discharge. Splitting of the hydrogen H β and H γ lines is applied for simultaneous determination of local electric field and temperature of excited H atoms in pure hydrogen and in argon-hydrogen mixture. Temperature measurements showed that, in pure hydrogen discharge, at least two groups of excited atoms exist: slow, with average energies in the range from 3.4 eV to 8.2 eV and fast, ranging between 80 eV and 190 eV. In argon-hydrogen discharge, excited hydrogen neutrals with average energies between 32 eV and 43 eV are detected only. The origin of these energetic neutrals is related to the presence of H + and H 3 + ions in pure hydrogen, and to the dominant role of H 3 + ion in argon-hydrogen mixture. For both gases, in the negative glow region, the increase of the exited hydrogen atoms temperature is detected and explanation suggested. For the electric field measurements in pure helium and helium-hydrogen mixture, the Stark splitting and shifting of the neutral helium 492.19 nm, 447.15 nm and 406.62 nm with respect to their forbidden counterparts is used. Good agreement between electric field measurements from these three helium lines is obtained.