Non-resonant inelastic X-ray scattering spectroscopy: A momentum probe to detect the electronic structures of atoms and molecules

Shu-Xing Wang,Lin-Fan Zhu

doi:10.1063/5.0011416

Abstract

Non-resonant inelastic X-ray scattering (NRIXS) is a new technique for atomic and molecular physics that allows one to measure the electronic structures and dynamic parameters of the ground and excited states of atoms and molecules in momentum space. There is a clearly understood physical picture of NRIXS, which reveals its remarkable advantages of satisfying the first Born approximation and being able to excite dipole-forbidden transitions. Various physical properties of atoms and molecules, such as their elastic and inelastic squared form factors, optical oscillator strengths, and Compton profiles, can be explored using NRIXS under different experimental conditions. In this paper, we review newly developed experimental methods for NRIXS, together with its characteristics and various applications, with emphasis on the new insights into excitation mechanism and other new information revealed by this technique. The intrinsic connections and differences between NRIXS and fast electron impact spectroscopy are elucidated. Future applications of this method to atomic and molecular physics are also described.

Highlights

Atomic and molecular dynamic parameters are closely related to electronic structure, i.e., to the wave functions of ground and excited states
We summarize recent developments in non-resonant inelastic X-ray scattering, and we limit our scope to applications in atomic and molecular physics
The importance of cross-checking the experimental results determined by IXS and energy loss spectroscopy (EELS) to obtain benchmark dynamic parameters of the valence-shell excitations of gaseous atoms and molecules will be pointed out

Summary

Introduction

Atomic and molecular dynamic parameters are closely related to electronic structure, i.e., to the wave functions of ground and excited states. Fast electron impact and inelastic Xray scattering have the merit of determining the electronic structures of the ground and excited states of atoms and molecules in momentum space, including the case of zero momentum transfer. A cross-check among the experimental results obtained by different methods can exclude possible systematic experimental errors and provide benchmark atomic and molecular data for use in simulation models and for testing theoretical methods. These tested theoretical methods and computational codes can be used to construct reliable atomic and molecular databases, which have wide applications across a number of disciplines, including plasma physics, fusion physics and engineering, astrophysics, condensed matter physics, materials science, chemistry, biology, and atmospheric sciences. We summarize recent developments in non-resonant inelastic X-ray scattering, and we limit our scope to applications in atomic and molecular physics

Methods

Results

Conclusion