05/25/02
Roueff Evelyne	Observatoire de Paris
LUTH, Place J. Janssen	SF2A-
92190	Meudon, F

Presentation 1 : Invited
Formation and excitation of H_2 in the interstellar space
Evelyne Roueff
A wealth of observational data on interstellar molecular hydrogen has recently been gathered both from ground based telescopes (CFHT, ESO, …) and the Infrared Space Observatory (ISO), via infrared emission, and from the Far Ultraviolet Spectroscopic Explorer (FUSE) via ultraviolet absorption. As interstellar hydrogen is mainly formed on dust grains and destroyed via photodissociation in translucent interstellar clouds, the FUSE observations may constrain the formation rate of H_2 on dust, a process whose efficiency is still poorly known. H_2 infrared emission on the other hand is produced in sources as diverse as Herbig-Haro objects, star-forming molecular clouds and their associated photon-dominated regions, planetary nebulae, supernovae remnants and X-ray excited gas. I will outline some recent observational results and emphasize the associated modelling attempts, focussing on the different physical mechanisms at work.

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