Interference quenching of a certain final vibrational state in resonant X-ray photoemission: A method to obtain geometrical information on the core-excited state

An interference quenching of the m = 1 final state vibrational line in the resonant Auger decay of N 1s* core-excited N2 is observed and analyzed. The intensity ratio between the m = 1 and m = 0 vibrational levels of the X 2 final state shows a surprising nonmonotonic variation as a function of frequency detuning, going through a minimum with a complete suppression of m = 1. We have developed a simple model which indicates a linear relation between the value of the detuning frequency for this minimum and the equilibrium bond distance of the core-excited state. This implies the possibility of determining the equilibrium bond distances for core-excited states to a high degree of accuracy. Simultaneously with the simple model we present a strict theory of the studied effect. This strict theory allows us to explore the accuracy of determining the bond length of the core-excited state from resonant Auger spectra. We obtain a weak influence of the core-hole lifetime on the determined bond length, whereas the number of intermediate vibrational states accounted for in the numerical simulations seems to be quite important