Hydrogen dissociation degree in the Grimm-type glow discharge measured by optical emission spectroscopy

The hydrogen dissociation degree is measured by means of optical emission spectroscopy in the cathode sheath of cylindrical abnormal Grimm-type DC glow discharge operating in the hydrogen–argon mixture at low pressure. The degree of dissociation, ranging from 80% in the close vicinity of the cathode and decreasing to 60% towards the negative glow, is obtained from the intensity ratio of the hydrogen Balmer H γ line and the diagonal Fulcher-α molecular bands. The cathode sheath thickness is extracted from the electric field strength distribution measured using Stark spectroscopy of the hydrogen Balmer H α line. An electron temperature of 2.7 eV in the negative glow region is estimated by observing the intensity ratio of the diagonal Fulcher-α bands and the H α line. Graphical Abstract