Application of $$\hbox {GK}^{{\mathbf {1}}} \Sigma ^{+}_{\mathbf {g}}$$, $$\nu ' = 0 \rightarrow \hbox {B}^{1} \Sigma ^{+}_{\mathbf {u}}$$, $$\nu '' = 0$$ hydrogen band for the axial temperature measurement in the cathode sheath region of an abnormal glow discharge

Abstract

In this paper, optical emission spectroscopy technique was used to measure rotational and gas temperature distribution in the cathode-sheath region of an abnormal glow discharge operated in hydrogen and hydrogen–argon mixtures. The rotational temperature of excited electronic states of H $$_{\mathrm {2}}$$ was determined from the R-branch of the $$\hbox {GK}^{\mathrm {1}}\Sigma ^{\mathrm {+}}_{g}$$ , $$\nu '= 0 \rightarrow \hbox {B}^{\mathrm {1}}\Sigma ^{\mathrm {+}}_{u}$$ , $$\nu ''=0$$ band and compared with published results for the Q-branch of the Fulcher- $$\alpha $$ diagonal band $$\hbox {d}^{\mathrm {3}}\Pi ^{\mathrm {-}}_{\mathrm {u}}$$ , $$\nu ' \rightarrow $$ $$\hbox {a}^{\mathrm {3}}\Sigma ^{\mathrm {+}}_{\mathrm {g}}$$ , $$\nu '' (\nu '=\nu ''=0$$ ). The population of excited energy levels, determined from the relative line intensities, was used to derive the rotational temperature of the ground state of hydrogen molecule. The boundary between the cathode sheath and negative glow region is determined using Stark polarization spectroscopy of the hydrogen Balmer alpha line. The thickness of the cathode sheath is estimated by fitting the experimentally determined distribution of electric field strength to a suitable model function. Temperature distributions along the axis of the cathode sheath are also reported and discussed. The distributions of temperature show that both bands give consistent and reasonable values for the rotational temperature and they both mutually agree within the estimated experimental uncertainties of 15%. The reported results contribute to the development of the spectroscopic method for gas temperature measurement in pure molecular hydrogen and in the gas mixture with argon.