I have been preforming experiments to study the diffusion of Hydrogen through Molybdenum. According to Sievert's law diatomic molecules would diffuse as atoms. But according to my experiments I notice that the flux of hydrogen is directly proportional to the pressure of hydrogen and not to the Square root of pressure. 1. Why do diatomic molecules disassociate when they get adsorbed on metal surfaces? 2. Is the chemical potential of hydrogen in the inner wall of the metal equal to the chemical potential of H in the outer wall? 3. How do I explain my observations?