Auger resonant Raman effect for dissociative core-excited states: General treatment and application to the HCl case

Abstract

We apply our recently developed explicitly time-dependent theory for one-step resonant excitation-deexcitation processes of core hole states in diatomic molecules to the case of purely dissociative intermediate states and exemplify it by application to $\mathrm{Cl}{2p}_{3/2}$ excitation in HCl. A main goal is the conceptual understanding of the influence of detuning of the exciting radiation away from the excitation resonances. The calculated spectra for decay to different final states (binding as well dissociative ones, as well as to hypothetical final states selected to illustrate certain points of the behavior), are very rich; their main features agree with experimental observations and previous calculations using other approaches. The spectra are dominated by a sharp asymmetric peak which does not shift with photon energy. While its previous designation as ``atomic decay peak'' is warranted to first order, we show that it contains contributions from throughout the evolution in the intermediate state, i.e., also from times and internuclear distances for which the molecule has not yet separated. Its width is given by the core hole lifetime. The broad ``molecular decay'' contribution to the spectra can be very complicated, depending on the final state potential and the exciting radiation tuning conditions. Its width is determined mainly by the Franck-Condon width of the intermediate state wave packet. For strong detuning it approaches the direct photoemission spectral shape. When these two features overlap, deep spectral holes develop which we explain by interference of different paths (atomic and molecular decays) to the same final state. These and other findings are discussed in a conceptual way.