Generalized Oscillator Strength for K-Shell Near Edge Structures in N₂

Abstract

Near-edge structures have recently attracted good amount of interest as a novel source of information on local structural properties of the matter. Their study in simple molecules is undertaken with the aim of fully clarifying the fundamental excitation mechanism and the nature of the structural parameters to which they are sensitive. The N₂ molecule in particular has been extensively investigated by using either photons and electrons as excitation sources, the main difference being in the possibility, for the electrons, to transfer a continuum of linear momentum K and of energy ε. Within the framework of the first Born approximation, the target response to the electron impact excitation is described in terms of a bidimensional generalized oscillator strength f(K,ε), whose equivalent in photoabsorption is the optical oscillator strenght f₀(ω). In the limit of K→0, or equivalently high incident electron energy and zero scattering angle, the G.O.S. converges to the O.O.S. and on this basis optically related quantities can be extracted from electron energy loss experiments and compared with photoabsorption experiments. In the region of K≠0, conversely, where also optically forbidden transitions are excited, unique information can be derived from the G.O.S. dependence on K.