MANY-ELECTRON THEORY OF PHOTOEMISSION
R. L. Martin, D. A. Shirley · eScholarship (California Digital Library) · 1975
I • I~ ' I '4 -3that if one'simply observed the attenuation of the photpn flux, the information obtained would pertain to a combination of absorption processes involving all the ionic states that are energetically accessible to the radiation.-Theadvantage of PES is that it allows the study of specific ionic states.This chapter will deal with the nature of these excited states, their energies, and the transition probabilities for reaching them via photon absorption.In Section II the basic theoretical formalism for the interaction of the radiation field with an N-electron system will be reviewed.The nature of the wavefunctions used to describe electronic states and the means of computing them is presented in Section III.In Section IV, the physical concepts which emerge from a study of the wavefunctions will be used to characterize the nature of the ionic states observed in PES.Section V will then analyze the photoionization crosssection in terms of the logical hierarchy of approximations commonly employed in cross-section calculations.The sum rule which relates the cross-section to the relaxation energy will also be discussed.In Section VI the orig~ and magnitude of the relaxation energy in a variety of systems will be examined and related to the physical and chemical properties of the species.The chapter ends with a brief discussion of the most commonly used approaches for estimating binding energies. II. INTERACTION WITH THE RADIATION FIELD AND PHOTOIONIZATIONWe begin by briefly reviewing the semiclassical treatment of the interaction of radiation with matter.As Schiff 1 points out, the term "semiclassical" refers to the assl.IDlption that the radiation field may be treated classically (within the framework of Maxwell's equations), whereas the system.ofparticles is treated quantum-mechanically.This appxoximation