  Autoionizing electronic states are common intermediates in processes
initiated by electron impact or high-energy radiation. These states belong to
the continuous spectrum of the Hamiltonian, and as such cannot be treated with
methods developed for bound electronic states. Here we propose a new model for
describing metastable electronic states, which combines discretized Feshbach
projection formalism and multireference perturbation theory and exploits
absorbing potential to generate the basis of the coupled valence state and
continuum. The results of benchmark calculations for a series of shape
resonances in polyatomic molecules are in good agreement with experimental and
theoretical reference values.
