Competing mechanisms in molecular hydrogen formation on silicates in conditions relevant
to the interstellar medium
Jean-Louis LEMAIRE
Université Cergy/LERMA
Résumé :
The most efficient mechanism of molecular hydrogen formation in the universe
is by association of H-atoms on the surface of interstellar dust grains.
The details of its formation and release processes from the grain are of
paramount importance in the physical/chemical evolution of the space
environments where it takes place. The fate of the 4.5eV released in
H2 formation is still puzzling: does it go into internal
energy/translational-kinetic-energy/grain heating ? The modality
of this energy release affects the ISM dynamics and evolution towards
stellar formation. We present results of the detection of the ro-vibrational
states of the just-formed H2 as it leaves a silicate surface.
We find, using REMPI-TOF, that excited molecules are ejected into the
gas phase immediately after formation over a much wider range of grain
temperature than anticipated. Our results can be explained by the presence
of two formation mechanisms operating in partially overlapping ranges
of grain temperature.
