Molecular Hydrogen Formation on Ice Under Interstellar Conditions
  The results of experiments on the formation of molecular hydrogen on low density and high density amorphous ice surfaces are analyzed using a rate equation model. The activation energy barriers for the relevant diffusion and desorption processes are obtained. The more porous morphology of the low density ice gives rise to a broader spectrum of energy barriers compared to the high density ice. Inserting these parameters into the rate equation model under steady state conditions we evaluate the production rate of molecular hydrogen on ice-coated interstellar dust grains. 
Hagai B. Perets, Ofer Biham, Giulio Manico, Valerio Pirronello, Joe   Roser, Sol Swords and Gianfranco Vidali