Measurement of hydrogen Balmer α line broadening and thermal power balances of noble gas-hydrogen discharge plasmas

Abstract

Line broadening of the hydrogen Balmer lines provides a sensitive measure of the number and energy of excited hydrogen atoms in a glow discharge plasma. The width of the 656.5 nm Balmer α line emitted from glow discharge plasmas having atomized hydrogen from pure hydrogen alone, hydrogen with magnesium or strontium, a mixture of 10% hydrogen and helium, argon, krypton, or xenon, and a mixture of 10% hydrogen and helium or argon with strontium was measured with a high resolution (±0.025 nm) visible spectrometer. It was found that strontium–hydrogen, helium–hydrogen, argon–hydrogen, strontium–helium–hydrogen, and strontium–argon–hydrogen plasmas showed significant broadening corresponding to an average hydrogen atom temperature of 25– 45 eV ; whereas, pure hydrogen, krypton–hydrogen, xenon–hydrogen, and magnesium–hydrogen showed no excessive broadening corresponding to an average hydrogen atom temperature of ≈3 eV . Since line broadening is a measure of the plasma temperature, and a significant difference was observed between these noble gases, the power balances of glow discharge plasmas of (1) pure krypton alone, (2) a mixture of hydrogen with argon or krypton and (3) a mixture of hydrogen and helium or argon with vaporized strontium were measured. The power emitted for power supplied to the glow discharge increased by 35– 83 W depending on the presence of helium or argon and less than 1% partial pressure of strontium metal in noble gas–hydrogen mixtures. Whereas, the chemically similar noble gas krypton alone or with hydrogen had no effect on the power balance. Catalyst atoms or ions which ionize at integer multiples of the potential energy of atomic hydrogen ( Sr, He + , or Ar +) caused an increase in power; whereas, no excess power was observed in the case of krypton which does not provide a reaction with a net enthalpy of a multiple of the potential energy of atomic hydrogen under these conditions. For a power input to the glow discharge of 110 W , the excess output power of mixtures of strontium with argon–hydrogen (95/5%), strontium with hydrogen, strontium with helium–hydrogen (95/5%), and argon–hydrogen (95/5%) was 75, 58, 50, and 28 W , respectively, based on a comparison of the temperature rise of the cell with krypton–hydrogen mixture (95/5%) and krypton alone. The input power was varied to find conditions that resulted in the optimal output for the strontium–hydrogen plasma. At 136 W input, the excess power significantly increased to 184 W . These studies provide a useful comparison of catalysts for the optimization of a catalytic reaction of atomic hydrogen which represents an important new power source.