Doppler spectroscopy of hydrogen Balmer lines in a hollow cathode water vapour and argon–water vapour glow discharge

Abstract

The results of Doppler spectroscopy of hydrogen Balmer lines in a stainless steel (SS) and copper (Cu) hollow cathode (HC) water vapour and argon–water vapour glow discharge are reported. The experimental profiles in water vapour discharge are fitted well by superposing three Gaussian profiles. The half widths of narrow and medium Gaussian are, in energy units, 0.2–0.5 and 3–4 eV for SS HC and 0.14–0.38 and 2.7–3.7 eV for Cu HC which is expected on the basis of earlier electron beam → H2O vapour experiments. The half width of the largest Gaussian in water vapour is 22 eV and 13 eV for SS and Cu HC, respectively. In argon–water vapour discharge three Gaussians are also required to fit experimental profiles. While half widths of narrow and medium Gaussians are similar to those in water vapour, the half width of the largest Gaussian is 37 eV and 28 eV for SS and Cu HC, respectively. The half widths of the largest Gaussian in water vapour and in argon–water vapour mixture indicate the presence of excessive Doppler broadening. The differences in width of the excessively broadened part of the line profiles with SS and Cu HC in water vapour and in argon–water vapour mixture are explained as a consequence of oxide formation at the cathode surface. This study is an attempt to extend and compare our earlier investigations of anomalous Doppler broadening in HC discharge operated with hydrogen isotopes or hydrogen mixtures with inert gases to hydrogen containing inorganic molecules.