Adsorption and recombination of hydrogen atoms on glass surfaces. Part 1.—Method of study and the mechanism of recombination at 77 and 273 K

Abstract

The mechanisms by which hydrogen atoms recombine on the surface of a 1 dm³ Pyrex glass bulb have been studied by following the changes in pressure during and after dissociation of molecular hydrogen at an incandescent tungsten filament. Experiments were conducted in a system capable of ultra high vacuum using hydrogen pressures in the range 10^–5–10^–3 N m^–2.

At 77 K, recombination occurred mainly as a result of collisions between gas phase atoms and adsorbed atoms (the Eley–Rideal process), with virtually no contribution from the recombination of adatoms (the Langmuir–Hinshelwood process). With the glass surface at 273 K, a weakly bound state of atomic hydrogen could be maintained on the surface only in the presence of gas phase hydrogen atoms. This weakly bound state constituted ≈ 3–10 % of the total adsorbed atomic hydrogen but was of considerable significance, being the major participant in both the Eley–Rideal and Langmuir–Hinshelwood processes occurring at this temperature.