Subnatural Linewidths in Core Level Excitation Spectra

We have measured a core excitation spectrum on the N2 1s->?* transition in which the experimental linewidth is limited by the instrumental resolution rather than by the lifetime of the core hole. The measurement is performed by recording the partial yield of resonant Auger electrons within a fixed kinetic energy window. The factors contributing to the line shape and the general applicability of the method are discussed.