Measurements of water molecule isotopomer concentrations in a discharge of inert gas with addition of H2O and D2 vapours by the method of external-cavity diode laser spectroscopy

Discharge plasma in inert gases with added water vapours and deuterium is studied by using the optimised diode laser spectroscopy with an external cavity. Formation of a spectrally dense grid of cavity transverse mode eigenfrequencies allows one to determine the parameters of Doppler broadening for absorption lines, a kinetic temperature of molecules, and their statistical sums. By using these parameters and the value of an absorption coefficient, correlations of concentrations are found for H₂O and HDO isotopomers at various ratios of plasma-forming gas components. An important contribution of initial gas molecules adsorbed on walls into the formation of plasma composition is stressed. It is found that the ratio of H₂O and HDO concentrations is the same at various ratios of H₂O and D₂ concentrations in plasma-forming gases and is constant during the discharge burning process.