Optical characteristics of the plasma of a glow discharge in a He/H2O mixture

The emission from the plasma of a steady-state electric discharge in a He/H2O mixture in the wavelength range 130-670 nm is investigated. It is shown that, at a water vapor partial pressure of P = 2.0-2.5 kPa, the discharge mainly emits within the range 306-315 nm. The emission consists of an OH (A-X; 0-0) 307.4-nm narrow peak and a broad band with a maximum at lambda (max) = 309.1 nm. As the partial pressure of water vapor decreases to 50-150 Pa, VUV emission at wavelengths of lambda = 186, 180, and 157 nm becomes dominant. In the visible region, H(alpha)656.3-nm and H(beta)486.1-nm spectral lines and Hel lines in the range 447.1-667.8 nm, which are of interest for diagnosing the plasma, prevail. The intensities of the main bands and spectral lines are determined as functions of the helium partial pressure and discharge current. (C) 2001 MAIK Nauka/Interperiodica.