Before revision: There are three main regions found on a spectrum generated by XAS data which are then thought of as separate spectroscopic techniques (Figure 2): The absorption threshold determined by the transition to the lowest unoccupied states: The X-ray Absorption Near-Edge Structure (XANES) introduced in 1980 and later in 1983 , also called NEXAFS ( Near-edge X-ray Absorption Fine Structure) which are dominated by core transitions to quasi bound states (multiple scattering resonances) for photoelectrons with kinetic energy in the range from 10 to 150 eV above the chemical potential, called "shape resonances" in molecular spectra since they are due to final states of short life-time degenerate with the continuum with the Fano line-shape.
After revision: There are three main regions found on a spectrum generated by XAS data which are then thought of as separate spectroscopic techniques (Figure 2): The absorption threshold determined by the transition to the lowest unoccupied states: The X-ray absorption near-edge structure (XANES) introduced in 1980 and later in 1983 and also called NEXAFS ( near-edge X-ray absorption fine structure),, which are dominated by core transitions to quasi bound states (multiple scattering resonances) for photoelectrons with kinetic energy in the range from 10 to 150 eV above the chemical potential, called "shape resonances" in molecular spectra since they are due to final states of short life-time degenerate with the continuum with the Fano line-shape.