DISSOCIATION OF SLOW POLYATOMIC-MOLECULES BY GRAZING SCATTERING AT SURFACES

We consider polyatomic molecules containing peripheral chains of valen ce groups, which slide along crystallic surfaces at grazing incidence. The periodically located Coulomb centres of the crystallic surfaces i nteract with the moving valence group dipoles like a time-dependent os cillation potential. This interaction can lead to multiple resonant vi brational excitations of the peripheral valence group dipoles. Accumul ation of such collective excitations in the valence group chains (exci mols) eventually can lead to the cleavage of particular bonds (trap bo nds) inside the molecule. A model for this complex process is presente d including a parameterised formula for the dissociation probability o f polyatomic molecules scattered by a surface at grazing incidence. Th e model is supported by the experimental observation of dissociation e nergy thresholds.