Slow electrons elastic scattering

Fig. 19. TOF distributions of (a) m/e = 28 and (b) m/e = 14, at = 36° and 60eV electron energy from the reaction C(3P) + C2H4 at E, = 7.4kcalmol-1. The m/e = 28 signal is due to elastically-scattered C2H4, while the m/e = 14 signal comes from dissociative ionization of elastically-scattered C2H4 (see text), (c) TOF distributions of m/e = 14 at 20 eV electron energy here the fast peak reflects CH2 from channel (3g) while the slow peak reflects the dissociative ionization of the C3H3 main product (channel (3a)).

The cross-section minimum in the Ramsaur-Townsend effect, which is present in slow electron-(Ar, Kr, Xe) scattering, is absent in the elastic scattering from He or Ne [100]. 

When slow electrons (energy less than about 300 eV) are directed normal to a surface, only a small fraction is elastically backscattered. The remaining electrons are backscattered after losing energy, or are absorbed in the crystal. Only the elastically scattered electrons, about 1 % of the incident number, produce the diffraction patterns with which we are concerned here. 

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