<i>Ab initio</i> Auger spectrum of the ultrafast dissociating 2p_3/2⁻¹σ* resonance in HCl

We present an <i>ab initio</i> theoretical method to calculate the resonant Auger spectrum in the presence of ultrafast dissociation. The method is demonstrated by deriving the L-VV resonant Auger spectrum mediated by the 2p_3/2^-1σ* resonance in HCl, where the electronic Auger decay and nuclear dissociation occur on the same time scale. The Auger decay rates are calculated within the one-center approximation and are shown to vary significantly with the inter-nuclear distance. A quantum-mechanical description of dissociation is effectuated by propagating the corresponding Franck-Condon factors. The calculated profiles of Auger spectral lines resemble those of atomic Auger decay but here the characteristic tails extend towards lower electron kinetic energies, which reflect specific features of the potential energy curves. The presented method can describe the resonant Auger spectrum for an arbitrary speed of dissociation and simplifies to known approximations in the limiting cases.