X-ray-absorption spectroscopy beyond the natural width measured in partial Auger yield mode

We report both experimental and theoretical studies on x-ray absorption measured using partial Auger yields of gas phase nitrogen, carbon monoxide, and oxygen molecules near the N 1s→ π*, O 1s→ π*, and O 1s→ π* regions, respectively. The main tool of our study is a two-dimensional map in which resonant Auger yields are plotted as a function of photon and kinetic energy. The partial yields of the three molecules are analyzed in detail by extracting profiles along various directions in the map. Narrowing of the absorption resonances is observed along the direction of constant kinetic energy. It is shown that such profiles are similar to the conventional x-ray-absorption spectrum for a broad class of molecules whose potential energy surfaces of the final and core-excited states are almost parallel. However, substantial differences with the conventional x-ray-absorption profiles are observed in the general case of nonparallel surfaces due to the lifetime vibrational interference. Here, we suggest a systematic way to eliminate the lifetime vibrational interference.