Fano meets nuclei: Configuration interaction theory explicitely including nuclear degrees of freedom

Electronic decay processes like the Auger-Meitner process and the Interparticle Coulombic Decay (ICD) are omnipresent and occur in areas like metallurgy, analysis of surfaces, semi-conductors, water, solvents, noble gas clusters and even in the active centers of proteins. These processes are initated by removal or excitation of a sub-outervalence electron, which can be achieved by, e.g., light in the XUV to x-ray range. These energies allow the creation of ultrashort laser pulses and hence time-resolved measurements with high time resolutions. So far, electronic decay processes were described by Fano's theory. However, this theory considers only the involved electronic states while neglecting the nuclear parts of the wavefunction. Especially in the case of ICD, though, the nuclear dynamics are required for an accurate description. We therefore present an analytical ansatz for the explicit inclusion of the nuclear wavefunction within the Born-Oppenheimer approximation into Fano theory. We thereby gain a model, which can serve for illustrative interpretations of electronic decay processes, in which nuclear motion is relevant.