Prof. Dr. Matjaž Žitnik (IJS, FMF): Resonant Auger spectrum of not too slow and not too fast decaying resonance: the L-VV spectrum of 2p-1sigma* state in HCl

An ab-initio L3-VV resonant Auger spectrum of 2p-1(3/2)sigma resonance in HCl is compared to the high resolution experimental spectrum in the 170-180 eV electron energy range. Since the lifetime of the Cl 2p hole is comparable to the time needed for HCl to dissociate and the potential energy curves of the molecular states are parallel only at large inter-nuclear distances R, none of the usual simplifications of the Kramers-Heisenberg formula is applicable for the calculation of the Auger lineshape over its full spectral range. The stationary Green function correlating vertical absorption and emission events in space is employed to generate the spectrum that agrees reasonably well with the state-of-the-art experimental data. While accurately calculated potential curves are a prerequisite for reliable estimation of the (Franck-Condon) overlap of the intermediate and final state molecular continua, the comparison with the experimental data shows the necessity to account for R-dependence of the partial electronic Auger decay rates. The demonstrated approach may be useful to decipher resonant Auger spectra whenever the electronic decay and molecular dissociation unfold on the same time scale.
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