ENERGY-TRANSFER PROCESSES AND MOLECULAR DEGREES OF FREEDOM IN THE COLLISION OF SF6 MOLECULES WITH THE GASE(001) SURFACE

It is shown that the use of an energy detector (cryogenic bolometer) to measure the angular distribution of an SF6 molecular beam scattered from the GaSe(001) surface gives direct information about the energy exchange processes. A careful analysis of the different contribution to the scattered normalized signals reveals a variety of unexpected and interesting features. Their behavior as a function of the surface temperature and of the beam velocity is presented and discussed. The role of the SF6 molecular rovibrations on the energy transfer mechanism has been assessed by comparison with similar measurements with a Xe beam. In fact, the different behavior between the atomic and the molecular scattering data supports the idea that the molecular degrees of freedom play a relevant role in the direct inelastic processes. To this conclusion one could not arrive measuring only the angular distribution of molecules as shown by some mass spectrometric measurements on graphite.