SIMBAD references

Physical conditions in dense and cold regions of interstellar clouds favour the formation of ice mantles on the surfaces of interstellar grains. It is predicted that most of the gaseous species heavier than H2 or He will adsorb on to the grains and will disappear from the gas phase, changing its chemistry, within ∼ 10⁹/nH yr. Nonetheless, many molecules in molecular clouds are not completely depleted in time-scales of 10⁵yr. Several speculative mechanisms have been proposed to explain why molecules stay in the gas phase, but up to now none is fully convincing. At the same time, these mechanisms are not mutually exclusive and we can still explore the effects of other possible processes. We speculate on the consequences of H2 coating of grains on the evaporation rates of adsorbed species. More experiments and simulations are needed to calculate the evaporation rate Eevap(X-H2).