Reaction of chlorine and molybdenum by modulated molecular beam mass spectrometry

Abstract

The reaction of molecular chlorine with polycrystalline molybdenum was studied by the modulated molecular beam mass spectrometry technique. Between 300 and 900 K, MoCl 2 was produced with a reaction probability of about 10 −3 on a chlorine-covered surface. At higher temperatures, the chlorine coverage decreased because of three direct reactions on the substrate metal: recombination to form Cl 2; direct desorption of atomic chlorine; and a second reaction channel to produce MoCl 2. Chlorine chemisorbed on the metal surface acquired sufficient mobility to move away from the spot illuminated by the incident molecular beam. By 1500 K, the only major processes remaining were chemisorption of incident Cl 2 with near-unity sticking probability followed by rapid desorption of atomic chlorine. A kinetic model of the reaction, including all of the component elementary steps, was developed and compared to the data.