X-ray and Electron Scattering Studies on Electronic Structures and Electronic Excitation Dynamics of Molecules

Abstract

X-ray and electron scattering experiments are powerful tools for investigating the electronic structures of molecules. The momentum transfer dependence of the scattering cross sections provides valuable information about the shape of molecular orbitals, correlated motion of electrons, vibronic effects on electronic excitations and so on. In this article, recent developments in x-ray and electron scattering studies on electronic structures and electronic excitation dynamics of molecules are reviewed. In particular, we focus on the following three topics. The rst topic is an x-ray scattering study on electron correlation. Total (elastic + inelastic) x-ray scattering intensity as well as inelastic scattering intensity are related to electron pair distribution function through Fourier transformation, and hence comparisons between observed and calculated x-ray scattering intensities allow us to make a critical assessment of whether or not electron correlation is properly taken into account in the theoretical wave function. The second topic is interference effects on electron momentum prooles studied using (e, 2e) electron momentum spectroscopy. An analysis of the measured electron momentum densities for the F 2p nonbonding orbitals of CF 4 has clearly shown the presence of oscillatory structure having information about the orientation in space of the constituent F 2p atomic orbitals. The third topic is electron energy loss spectroscopy (EELS) studies of vibronic effects on electronic excitations in molecules. Examining the momentum transfer dependence of the EELS cross section makes it possible to see coupling between electronic states. By using this method we have revealed the roles of vibronic coupling in some valence-shell electronic excitations in CF 4 and CO 2. Keywords: x-ray scattering, electron energy loss spectroscopy, electron momentum spectroscopy, generalized oscillator strength 1. HOMO LUMO X projectile X