Line Narrowing in Photoemission by Coincidence Spectroscopy

We present photoemission spectra from the $3p$ level of Cu(100) obtained in coincidence with the M₃VV Auger line. The $3p$ level is narrowed from its 2.2-eV core-lifetime-broadened width to 1.0 eV, representing the intrinsic width of the ¹G Auger final state. The core line changes its energy within the 2.2-eV envelope as the Auger coincidence energy is changed, conserving the sum of Auger-electron and photoelectron kinetic energies.