Ab initio calculations of molecular resonant photoemission spectra

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An ab initio method for calculations of molecular resonant photoemission (RPE) spectra is described. The method includes a multicenter expansion of both the dipole matrix element—direct emission—and the Hamiltonian matrix element between the resonant state and the autoionizing states—resonant emission. These quantities are relevant for the description of the process both in the two-step model, where the spectrum is computed at the resonance energy only, and in the one-step model where, by a K-matrix approach, the direct-to-resonant interference is taken into account and the electronic line profile is fully described. The resonant two-electron matrix elements are evaluated over the core-excited relaxed orbitals with the outgoing Auger electron orbital expanded on an augmented multicentered Gaussian basis set. Stieltjes imaging is shown to work excellently for such Gaussian basis sets giving correct continuum normalization matrix elements even for RPE electron energies as high as 100–1000 eV. A numerical investigation is carried out for the participator decay of the C 1s→π* and O 1s→π* states of CO.