Interaction of Hydrogen and of Nitrogen with a Molybdenum Ribbon

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Abstract
Adsorption and desorption studies—by flash‐filament and ion gauge techniques—gave information on surface coverages, sticking probabilities, atom formation, and surface mobilities for the interaction of gases with a molybdenum ribbon. For hydrogen, saturation surface coverages were independent of pressure (10—8—10—5 mm Hg), within experimental errors, but depended strongly on temperature (225°—500°K). Adsorption below 320°K proceeded in two steps. Two layers were successively adsorbed and completed at 320° and 225°K, respectively; each contained close to two hydrogen atoms per surface molybdenum atom. The sticking probability was 0.35; it remained constant during the formation of the first layer. At about 700°K, no measurable amounts of hydrogen were retained on the ribbon surface, but the kinetics of atom formation above 1200°K suggested that traces of hydrogen might be adsorbed at much higher temperatures. Finally, adsorbed hydrogen was readily replaced by other gases, such as nitrogen, even at room temperature. For the adsorption of nitrogen, the saturation surface coverage decreased only about 30% from 225°—710°K; its value at room temperature was about one nitrogen atom per surface molybdenum atom. The initial sticking probability, in the same temperature range, decreased from 0.7 to 0.2.