Jean Louis Lemaire, LAMA, Observatoire de Paris-Meudon (France)

	From star forming regions to laboratory astrophysics


Summary: Large amounts of molecular hydrogen are observed in different
regions of the interstellar medium (ISM): dark clouds, star forming region,
reflection nebulae... How this molecular hydrogen has been formed is one of
the problem the astrophysicists have to deal with. A commonly accepted
assumption is that the formation of H2 takes place through heterogeneous
reactions at the surface of interstellar dust grains or of their icy
mantles. The surface recombination of H atoms releases about 4.5 eV of
energy which is then distributed between the grain and the translational
and internal (rovibrational) of the desorbed molecule. In particular
experimental data concerning the internal energy state of nascent H2
molecules are still scarce or conspicuously absent. ISM models (PDRs or
shock-driven) require the use of such data which are of fundamental
importance with respect to the energy balance in the ISM. An experimental
facility devoted to the study of molecular hydrogen formation on surfaces
that mimics dust grains under physical conditions relevant to the ISM has
been built in our laboratory. I will present the first experiments
concerning the formation, adsorption and desorption processes of hydrogen
on amorphous water ices. A very interesting isotopic effect has been
observed which may have important consequences for the chemistry in the
ISM, particularly concerning the formation of deuterated molecules.

Wednesday January 26th, at 11am