Surface Recombination of H Atoms on Pyrex in Medium-Pressure Hydrogen Plasma

The probability of heterogeneous recombination of hydrogen atoms, γH, on the surface of a Pyrex tube in a direct current glow discharge in pure hydrogen at medium pressure (2–7 Torr) has been measured as a function of the discharge pressure and current for two wall temperatures. It has been found that the recombination probability does not depend on the discharge pressure and current under the condition of preliminary training of the tube in a hydrogen discharge. The γH value decreases during the tube training with a characteristic time of reaching a steady-state value of ~30 min. Analysis of a possible recombination mechanism using quantum chemical methods shows that the recombination of hydrogen atoms on the Pyrex surface is associated with OH radicals and oxygen vacancies on the surface, and the dynamics of γH can be explained by the decay of surface OH radicals during tube training.