Resonances in optical excitation functions

Abstract

The collision between an electron and an atom may result in the excitation of the atom to a state from which it can decay with the emission of light. The dependence on electron energy of the cross-section for excitation is called the optical excitation function. In this review we discuss the effect on the optical excitation function of the attachment of the impacting electron to the atom to form a temporary negative ion or resonance. We describe the special techniques needed for the observation of these resonances and show some examples. We discuss different types of resonance and suggest how some of them may be grouped in series. We include a list of all papers which report the measurement of optical excitation functions using velocity selected electrons.