SURFACE-INDUCED DISSOCIATION IN H-2(-SPECTROSCOPY() COLLISIONS STUDIED WITH ION IMPACT ELECTRON)

The electronic transition processes in slow collisions of small molecu lar ions with metal surfaces are discussed briefly. Examples will be g iven where molecular dissociation is induced by electronic transitions between the projectile and the surface. It will be demonstrated how i nformation on surface-induced dissociation (SID) can be obtained from ion impact electron spectroscopy. For slow collisions (mostly 50 eV) o f H-2(+) with tungsten surfaces the following channels for SID can be identified from the analysis of the ion impact electron spectra: (1) o n clean tungsten, the neutralization of the projectile ions into the r epulsive state H-2(b(3) Sigma(u)(+)), both resonantly and by Auger cap ture; and (2) for alkali covered tungsten, in addition to direct H-2(b (3) Sigma(u)(+)) population, both Auger de-excitation to H-2(b(3) Sigm a(u)(+)) and mechanical dissociation of hydrogen states, correlating w ith H(n = 2) + H(1s). (C) 1998 Elsevier Science B.V.