Electron resonances in DIET

The appearance of peaks or maxima in desorption yield functions, obtained b y 5 to 20 eV electrons impinging from vacuum onto atomic or molecular solid films, reveals the formation of transient anions (i.e. electron resonances ) at specific energies. Depending on the interaction of the incident electr on with a particular atom or molecule and with the surrounding medium, the transient anion can cause desorption of a stable anion and one or more neut ral fragments or only neutral particle ejection. The former process occurs when the transitory anionic state dissociates before autoionization, wherea s decay by electron emission can, under certain circumstances, result in ne utral atom or molecule desorption. Details on these mechanisms are given in this article. They are illustrated from desorption yield functions recorde d for 5-20 eV electron impact on thin film targets made of pure Ar, CO2, D2 O and mixtures of Ar with H2O, O-2 and n-hexane. (C) 2000 Elsevier Science B.V. All rights reserved.