Isotopic segregation of molecular hydrogen on water ice surface at low temperature

Experimental studies of adsorption and desorption of molecular hydrogen on an amorphous porous solid water ice surface between 10 and 35 K reveal a very efficient isotopic segregation process. A statistical model, which take into account thermodynamic aspects of adsorption sites and isotopic competition, is proposed to understand the enhancement of deuterium fractionation. This mechanism could play a key role in chemistry at the surface of interstellar dust grains.