Photoionization of polyatomic molecules in the region of Feshbach resonances and beyond

Résumé

We have evaluated total and partial photoionization cross sections, asymmetry parameters, and molecular-frame photoelectron angular distributions (MFPADs) of polyatomic molecules by using the XCHEM methodology. This method accounts for electron correlation in the ionization continuum, which allows to describe Feshbach resonances and their autoionization decay. We have identified a large number of Feshbach resonances, some of them previously unknown, for which we provide energy positions and widths. Manyof these resonances lead to pronounced peaks in the photoionization spectra, some of them remarkably wide, which should be observable in high-energy resolution experiments. We show that, in the vicinity of these peaks, bothasymmetry parameters and MFPADs vary very rapidly with photoelectron energy, which, as in atoms and simpler molecules, reflects the interference between direct ionization and autoionization, which is mostly driven by electroncorrelation