Recent developments in electron momentum spectros-copy of atoms and molecules

Abstract

The application of electron momentum Spectroscopy to obtaining detailed information on the dynamic structure of atoms and molecules is discussed. As well as electron binding energies the method yields pole strengths and one electron momentum densities, which are given by the square of the momentum space overlap function between the initial N-electron target state and the final (N-1)-electron ion state. Its ability to provide wavefunction mapping, in terms of the independent particle representation of a manybody system in momentum space, is investigated for valence electrons. EMS also provides a quantitative measure of correlation effects in both the initial and final electron states. These correlation effects can significantly change the momentum densities for the “orbital” wavefunctions, i.e. for transitions with pole strengths close to unity. They also give rise to transitions forbidden in the independent particle approximation. The momentum densities for these transitions provide extremely sensitive tests of manybody theories. The sensitivity of the technique as a probe of electronic wavefunctions is discussed in some detail with particular reference to some recent work on both atoms and molecules.