 The vibrational component is produced by the excitation of low energy vibrational modes both in the initial and in the final state.Finally, inhomogeneous broadening can originate from the presence of unresolved core level components in the spectrum.In a solid, inelastic scattering events also contribute to the photoemission process, generating electron-hole pairs which show up as an inelastic tail on the high BE side of the main photoemission peak.